The Lower Cretaceous Figuera Lava 

and Fajardo Formation in the 

Stratigraphy of 

Northeastern Puerto Rico

By REGINALD P. BRIGGS

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1372-G

Prepared in cooperation "with the 

Commonwealth of Puerto Rico 

Department of Public Works and 

Economic Development Administration

The Figuera Lava and the overlying 

Fajardo Formation are redescribed and 

assigned to the Lower Cretaceous Series
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress catalog-card No. 73-600070

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973

For sale by the Superintendent of Documents, U. S. Government Printing Office

Washington, D. C. 20402 

Stock Number 2401-00319
CONTENTS

Page

Abstract...................................................................................................................... Gl

Introduction .............................................................................................................. 1

Figuera Lava ............................................................................................................ 3

Fajardo Formation .................................................................................................. 6

Regional correlations .............................................................................................. 9

References ................................................................................................................ 10

ILLUSTRATION

FIGURE 1. Map of part of northeastern Puerto Rico showing the general 

distribution of the Figuera Lava and Fajardo Formation 

relative to younger rocks ................................................................ G2

TABLE

TABLE 1. Recent development of nomenclature for stratigraphic units

in northeastern Puerto Rico ............................................................ G4

ill

CONTRIBUTIONS TO STRATIGRAPHY

THE LOWER CRETACEOUS FIGUERA 

LAVA AND FAJARDO FORMATION

IN THE STRATIGRAPHY OF 

NORTHEASTERN PUERTO RICO

By REGINALD P. BRIGGS

ABSTRACT

The Figuera Lava, the oldest stratigraphic unit now recognized in northeastern Puerto Rico, and the overlying Fajardo Formation are redescribed and the 

name Figuera redefined and reinstated for formal use. Previously, lower Tertiary strata some distance from the type areas of the Figuera and Fajardo were 

correlated with the units by reconnaissance. Recent detailed mapping and 

paleontology now place the Figuera and Fajardo in the upper part of the Lower 

Cretaceous Series. The Figuera Lava is correlated tentatively with an as-yetunnamed chemically similar volcaniclastic sequence in central Puerto Rico. 

Overlying this sequence is the Torrecilla Breccia, which is generally equivalent 

in time stratigraphy to the Fajardo Formation.

INTRODUCTION

In his report on the initial geological reconnaissance of the New 

York Academy of Science's "Scientific Survey of Porto Rico and the 

Virgin Islands," Berkey (1915, p. 61) referred to thin-bedded rocks 

in the vicinity of the town of Fajardo (fig. 1) as the Fajardo shales. 

This name was retained by Meyerhoff and Smith (1931, p. 284-288) 

in mapping the "Fajardo District" (an informally defined geographic 

unit approximating the area shown in fig. 1), and they named the 

underlying andesite lava unit the Figuera formation, after a point 

labelled Punta Figueras on recent maps.

Near Rio Piedras, about 40 km west of Fajardo (fig. 1), thinbedded rocks similar to those exposed at Fajardo rest on rocks similar 

in some respects to those near Punta Figueras. Meyerhoff and Smith 

extended the Fajardo and the Figuera to include the similar rocks at 

Rio Piedras and assigned the Figuera and Fajardo to the Upper CreGl
G2 CONTRIBUTIONS TO STRATIGRAPHY
FIGUERA LAVA AND FAJARDO FORMATION, PUERTO RICO G3

taceous Series. Kaye (1959, p. 22-29) accepted this correlation with 

reservations in his report on the San Juan metropolitan area, in which 

he applied the names Figuera volcanics and Fajardo formation to the 

rocks near Rio Piedras. He referred the Figuera and Fajardo of the 

Rio Piedras area to the Paleocene or Eocene on the basis of paleontological data more recent than those available to Meyerhoff and Smith.

More recently, a reconnaissance study by Berryhill, Briggs, and 

Glover (1960, p. 141-143) clearly demonstrated that the rocks at 

Fajardo and those near Rio Piedras are unrelated. In their report, the 

Fajardo of Kaye was not included in the Fajardo Formation, and by 

inference the Figuera of Kaye also was not included in the underlying 

Figuera Lava. The Fajardo was assigned a Late Cretaceous age 

(Berryhill and others, 1960, p. 143). Pease (1968, p. 40-46) renamed 

the former Figuera and Fajardo of the Rio Piedras area the Guaracanal Andesite and Rio Piedras Siltstone, respectively (fig. 1).

Detailed mapping now is complete in much of northeastern Puerto 

Rico, and a formal stratigraphic succession has been established for 

the strata between San Juan and Fajardo. Table 1 compares the 

stratigraphic positions formerly assigned to the Figuera and Fajardo 

with their positions as now known.

Other stratigraphic names used in the "Fajardo District" by 

Meyerhoff and Smith (1931) included the Guzman formation, Hato 

Puerco tuffs, Guaynabo formation, La Muda Limestone, Rio conglomerate, Luquillo formation, Trujillo Alto limestone, Juan Ascencio 

member of the Fajardo shales, and San Diego formation. Rocks overlying the Fajardo Formation in the vicinity of Cabezas de San Juan 

(fig. 1) were included in the San Diego formation (Meyerhoff and 

Smith, 1931, p. 289-290), but the name San Diego in current usage 

is applied to an entirely different rock unit elsewhere in Puerto Rico 

(Glover, 1961). The strata resting on the Fajardo now are included 

in the Tabonuco Formation (Seiders, 1971, p. 8-11). The Hato 

Puerco, Guaynabo, La Muda, and Trujillo Alto have been redescribed 

and adopted for current use by Kaye (1959), Pease (1968), and 

Seiders (1971). The Guzman, Rio, Luquillo, and Juan Ascencio have 

been abandoned.

FIGUERA LAVA

The Figuera Lava is here redefined and reinstated for a thick series 

of andesitic lavas that crop out in the hills west of Punta Figueras, 

the general type area of the Figuera formation originally designated 

by Meyerhoff and Smith (1931, p. 284-285).

Although recent maps label the point as Punta Figueras, a review 

of old maps shows a development of the name from Punta Figueroa to 

Punta Figuera to Punta Figueras. Meyerhoff and Smith were correct
G4 CONTRIBUTIONS TO STRATIGRAPHY

TABLE 1. Recent development of nomenclature for stratigraphic units in northeastern Puerto Rico

[Kaye's (1959) nomenclature was for the southeastern part of the San Juan metropolitan area. 

Indicated present usage is from that area eastward along Hwy. 3 to Punta Figueras, after 

Pease (1968), Seiders (1971), and this report]

Kaye (1959)

Fajardo formation.1 

Figuera volcanics.1

Trujillo Alto limestone.3 

Monacillo formation.4

Frailes formation.4

Guaynabo formation.1

Hato Puerco tuff. 1

Present usage

Rio Piedras Siltstone.2 

Guaracanal Andesite.2

Monacillo Formation.5

Frailes Formation.6

Martin Gonzalez Lava.7

Canovanas Formation.8 

Cambalache Formation.8

Hato Puerco Formation.9

Tabonuco Formation.10 

Fajardo Formation. 11

Figuera Lava.11

Age

Tertiary (Eocene? 

and Paleocene) .

Early Tertiary (?) and 

Late Cretaceous 

(Maestrichtian or 

Campanian, possible 

Paleocene in 

uppermost part).

Late Cretaceous 

(Campanian) .

Late Cretaceous 

(early Campanian 

to Santonian).

Late Cretaceous 

(Santonian to 

Cenomanian) .

Early Cretaceous 

(Albian).

Early Cretaceous 

(Albian?).

1 Adopted from Meyerhoff and Smith (1931).

2 Described and renamed by Pease (1968).

3 Adopted from Berkey (1915).

4 Described and named by Kaye (1959).

5 Trujillo Alto Limestone Member redefined and included in upper Monacillo Fm by Pease (1968).

8 In the area south of Rio Piedras, Pease (1968) did not recognize the Frailes Fm, and included 

these rocks in the upper part of the Guaynabo Fm. The Frailes Fm, however, was recognized by 

Seiders (1971) in the area east of Rio Piedras.

7 Originally described as a member of the Guaynabo Fm by Pease (1968). Raised to formational rank by Seiders (1971).

8 Named by Seiders (1971). Chiefly equivalent to middle and lower parts of the Guaynabo Fm 

as used by Kaye (1959) and Pease (1968) in the area south of Rio Piedras. 

8 Redefined by Seiders (1971).

10 Described and named by Seiders (1971).

11 Here redescribed. Names' retained, following original usage of Berkey (1915) and Meyerhoff 

and Smith (1931).

at the time of their mapping, so their form of the name is retained 

(American Commission on Stratigraphic Nomenclature, 1961, Art. 

12(b),p. 652-653).

The lithologic term "lava" is preferred to "formation" because 

recent detailed mapping in the Fajardo quadrangle (fig. 1) by the 

present writer has demonstrated that lava is the predominant rock 

type of the unit. The term "volcanics" was used to describe the 

Figuera only in the Rio Piedras area, where the name Figuera no 

longer is valid.

Meyerhoff and Smith designated no type section. The series of 

exposures along Hwy. 982 in the Fajardo 7^-minute quadrangle
FIGUERA LAVA AND FAJARDO FORMATION, PUERTO RICO G5

between 50,740 N., 233,580 E. and 50,660 N., 233,720 E.1 (fig. 1, loc. 

1) is here so designated. In this section, fresh residual boulders of 

Figuera Lava are exposed in place in a matrix of weathered Figuera. 

The lava is composed of sparse, small (about 2 mm long) phenocrysts 

of plagioclase set in a very finely crystalline groundmass. Elsewhere, 

most of the lava is similar to that in the type section, but locally it is 

amygdaloidal, phenocrysts are larger (as much as 10 mm long) and 

are moderately abundant, and the groundmass is coarser. In a few 

outcrops the lava has grayish red and dark gray layers a few millimeters wide, the contacts of which range from gradational to sharp. 

These atypical Figuera rocks have not been examined in detail. However, they bear a superficial resemblance to welded ash-flow deposits, 

such as those described by Berryhill (1965, p. 51-58).

Conspicuous in the type section are veins of smoky "bull" quartz 

several centimeters wide. These were introduced along joints approximately parallel to as well as normal to the regional gross layering of 

the rocks. Smoky quartz also is present in the type section as large, 

apparently randomly distributed blebs.

Although veins and blebs of quartz are present throughout much 

of the rest of the Figuera Lava, they are not as common everywhere 

as they are in the type section. Quartz veins cut across pillow structure in Figuera Lava outcrops at Punta Mata Redonda (fig. 1) where 

interpillow material is composed chiefly of quartz. The veins and 

blebs of quartz in the Figuera may be deuteric rather than regional 

phenomena, because quartz veins are rare in the adjacent overlying 

Fajardo Formation. In outcrops of Figuera Lava along the southern 

border of the Fajardo quadrangle (fig. 1), and locally elsewhere, 

there also are large, widely-spaced, irregular blebs and some veins of 

a pale yellowish-green intimate mixture of quartz and epidote. Locally 

in the southwestern part of the quadrangle, the Figuera has been 

altered to a pyritic hornfels.

Pillow structure, although a striking feature of Figuera Lava outcrops at Punta Mata Redonda and a few other places, is not characteristic of the unit as a whole.

Lava probably makes up most of the Figuera, but lava breccia and 

intercalations of thin- to medium-bedded2 well-stratified tuffaceous 

sandstone and siltstone and medium- and thick-bedded hyaloclastic 

tuff3 also are found within the unit. The Figuera Lava is essentially a

1Puerto Rico rectangular coordinate system in meters. Tick marks for this system are placed 

on the margins of all U.S. Geological Survey topographic maps of Puerto Rico.

2Layering thicknesses after Ingram (1954): in centimeters more than 100, very thick; 30-100, 

thick; 10-30, medium; 3-10, thin; 1-3, very thin; 0.3-1, thickly laminated; less than 0.3, thinly 

laminated.

'Terminology as used by Briggs, 1969, p. 2-6.
G6 CONTRIBUTIONS TO STRATIGRAPHY

sequence of many lava flows, some probably several hundred meters 

thick and some having pillow structure, interlayered with marine 

volcaniclastic units ranging from very thin to tens of meters thick.

Only the upper part of the Figuera Lava is included in the Fajardo 

quadrangle (fig. 1); only that part has been mapped in detail at the 

time of writing (1972). Reconnaissance to the south suggests, however, that the unit grades downward from andesite to dacite, a chemical change similar in trend to that found in rocks of probable similar 

age in central Puerto Rico (Lynn Glover 3d, written commun., 1967). 

If the dacitic rocks to the south ultimately are not separated from the 

Figuera Lava, then the Figuera Lava may be the oldest stratigraphic 

unit exposed in northeastern Puerto Rico; the dacitic terrane to the 

south is highly faulted, and the base of the dacite sequence may be 

concealed by faulting. The present writer found no good exposures 

of the upper contact of the Figuera Lava. However, because the 

Figuera is a marine unit, because rocks in the overlying Fajardo Formation also have typical marine layering, and because the lower 

Fajardo contains no conglomerate, it is concluded that the contact 

between the two units is conformable within a continuous marine 

sequence.

In the Fajardo quadrangle, the Figuera Lava section is estimated 

to be at least 1,200 m thick. If the underlying dacitic rocks to the 

south are not separated from the Figuera, the Figuera Lava may total 

several thousand meters in thickness.

Age. No fossils have been recovered from the volcaniclastic rocks 

of the Figuera Lava, and no radiometric age determinations have 

been made on Figuera rocks. However, the overlying Fajardo Formation probably is entirely latest Early Cretaceous (Albian), so the 

Figuera also is Early Cretaceous. It may also be Albian, for great 

thicknesses of lava can accumulate in relatively short intervals of 

geologic time.

FAJARDO FORMATION

The Fajardo Formation is here redescribed as the name of the thick 

volcaniclastic unit that underlies much of the Fajardo quadrangle 

(fig. 1). The general type area was designated by Berkey (1915, 

p. 61) and accepted by Meyerhoff and Smith (1931, p. 285-288) as 

the hills around the town of Fajardo (fig. 1). This type area also is 

accepted here, but it now is recognized that some of the area near the 

town is underlain by calcareous rocks assigned to the Tabonuco Formation (fig. 1; Seiders, 1971, p. 8-11).

Meyerhoff and Smith considered that thin-bedded fine-grained rocks 

like those at Fajardo predominate in the unit. However, a large part 

of the Fajardo Formation is composed of volcaniclastic rocks coarser
FIGUERA LAVA AND FAJARDO FORMATION, PUERTO RICO G7

than those in the type area. North of a line running generally westnorthwest from Punta Figueras through the village of Sabana (fig. 1), 

Eduardo Aguilar and the present writer were able to map four 

informal members in the Fajardo. These are, from bottom to top, 

(a) a lower coarse-grained volcaniclastic member, (b) a lower finegrained well-stratified member, (c) an upper coarse-grained volcaniclastic member, and (d) an upper fine-grained well-stratified member. 

South of this west-northwest line, the Fajardo Formation was not 

divided because poor access and poor exposures make identification 

of these informal members difficult.

Member a is about 1,600 m thick, and is composed of thick- and 

very thick bedded tuff breccia interlayered with prominent but subordinate units a few meters thick that contain thin- to thick-bedded 

tuffaceous sandstone and siltstone and thick-bedded coarse tuff. The 

siltstone commonly is cherty. Typical rocks of member a are well 

exposed along Hwy. 982, between 50,870 N., 232,860 E. and 50,900 

N., 232,050 E. (fig. 1, loc. 2), near the base of the Fajardo Formation.

Member b is composed chiefly of cherty tuffaceous siltstone and 

sandstone and ranges from about 130 m to about 500 m in thickness. 

As mapped by Aguilar and the present writer, it includes the type 

locality of the formation, placed by Meyerhoff and Smith (1931, 

p. 287) "one kilometer south of Fajardo." This is a small group of 

quarried hills centering about 54,070 N., 235,120 E. (fig. 1, loc. 3). 

Their description of these rocks can hardly be improved upon:

The beds are thinly stratified, and the closely spaced joints normal to the bedding planes give them a blocky fracture. Few of the layers exceed four inches 

[10 cm] in thickness, and most of them average about two [5 cm]. The rocks 

are exceedingly fine grained, and under the microscope the individual particles 

which can be isolated consist chiefly of angular fragments of volcanic glass, and, 

to a less extent, of mineral grains. The minute grains which compose the 

groundmass exhibit the polarization of quartz***. The buff color, which is such 

a striking feature of the formation in its deeply weathered exposures in the 

coastal areas, is due to the presence of interstitial hematite. Weathered specimens have an unusually low specific gravity, a feature which, in microscopic 

sections, may be traced to the abundance of cavities, formerly occupied by 

minute Foraminifera that have been dissolved in the course of rock decomposition.

(Meyerhoff and Smith, 1931, p. 288). The blocky fracture noted 

above causes development of a soil bearing small prisms of weathered 

rock. Exposures of fresh rock are relatively rare. Centers of some 

prisms in the soils are fresh and are neutral light to dark gray.

Member c is 800 to 1,100 m thick and bears a distinct resemblance 

to member a, except that it includes a higher proportion of thickbedded coarse tuff and somewhat fewer and generally thinner interlayered zones of thin-bedded sandstone and siltstone. Its tuff breccias
G8 CONTRIBUTIONS TO STRATIGRAPHY

are generally finer than those in member a; fragments are rarely more 

than 10 cm in diameter. No one really good section typically exposes 

member c, but relatively representative outcrops may be seen along 

Hwy. 985 between 55,000 N., 232,320 E. and 55,070 N., 232,590 E. 

(fig. 1, loc. 4a) and along Hwy. 988 between 55,240 N., 229,030 E. 

and 55,240 N., 229,780 E. (fig. 1, loc. 4b).

Member d is 170 to 250 m thick and lithologically is similar to 

member b, except that some cherty siltstones are black when fresh. 

A characteristic of member d, shared to a somewhat lesser extent by 

member b, is disturbed bedding interpreted as the result of penecontemporaneous submarine slump. A typical section where the thinbedded fine-grained rocks of d are well exposed is in a quarry on Hwy. 

991 at 58,130 N., 227,100 E. (fig. 1, loc. 5). In this quarry one of the 

better examples of penecontemporaneous slump is seen in a zone 

about 2 m thick paralleling gently dipping stratification. In this zone, 

blocks of typical sandstone and siltstone set in a clay matrix are 

contorted and fractured. Both member b and member d locally contain rare thick beds of tuff and fine breccia.

The undivided Fajardo south of the Sabana-Punta Figueras line 

contains tuff breccia, tuff, and tuffaceous cherty sandstone and siltstone, generally similar to the rocks north of the line in overall relative 

proportions but perhaps somewhat coarser on the average. The complex structure of the region makes accurate thickness measurements 

difficult, but the undivided Fajardo probably is more than 3,000 m 

thick.

The Fajardo Formation is largely noncalcareous, although it does 

contain some sporadic calcareous sandstone and siltstone beds 

throughout and some calcareous tuffs in the upper part of member c. 

The nature of its layering and the presence of marine fossils indicate 

that the Fajardo was deposited in a marine environment.

The report of Berryhill, Briggs, and Glover (1960, p. 143, fig. 6) 

can be interpreted to infer that the Aguas Buenas Limestone Member 

is in the basal part of the Fajardo Formation. This interpretation was 

not intended and has been rejected formally by the present writer 

(Briggs, 1969, p. 15). The Aguas Buenas Limestone Member is in the 

base of the Torrecilla Breccia (Briggs, 1969, p. 11-12) which is 

referred to in a following section.

The Fajardo rests on the Figuera Lava with apparent conformity 

and is overlain conformably by the Tabonuco Formation. The 

Fajardo-Tabonuco contact is gradational; the upper Fajardo contains 

some calcareous beds similar to those that compose most of the 

Tabonuco, whereas the lower Tabonuco contains subordinate cherty 

layers like those typical of the upper Fajardo (Seiders, 1971, p. 10).

Age. The Fajardo Formation was considered Late Cretaceous by
FIGUERA LAVA AND FAJARDO FORMATION, PUERTO RICO G9

Meyerhoff and Smith (1931, p. 266). Berryhill, Briggs, and Glover 

(1960, p. 143) were more specific, placing the age range of the Fajardo 

(exclusive of the rocks near Rio Piedras erroneously so labelled) as 

probably Cenomanian to Turanian or Coniacian (early Late Cretaceous). On the basis of fossil collections by N. F. Sohl and others, 

however, Seiders (1971, p. 11) now places the overlying Tabonuco 

Formation in the Lower Cretaceous Albian Stage, and recent determinations from the Fajardo Formation are compatible.

W. A. Cobban identified an ammonite collected by the present 

writer from the Fajardo Formation type locality (54,070 N., 235,120 

E.) as Manuaniceras, possibly M. carbonarium (Gabb), placing member b at "about the top of the middle Albian" (W. A. Cobban, written 

commun., 1967). In a collection from member d made by V. M. 

Seiders, Cobban (written commun., 1966) tentatively identified 

Oxytropidoceras sp., indicating a possible Albian age.

In summary, recent studies of fossil collections from the Tabonuco 

Formation, overlying the Fajardo Formation, place the Tabonuco in 

the Albian Stage (Seiders, 1971, p. 11). In the Fajardo Formation 

itself, one collection is quite definitely Albian, and another is suggested as Albian. Because member b, about in the middle of the 

Fajardo Formation, probably is middle Albian, it is not unreasonable 

to infer that the lower part of the formation also is Albian. However, 

the base of the Fajardo possibly could be older than Albian.

REGIONAL CORRELATIONS

The volcanic and plutonic terrane of Puerto Rico is divided into 

northeastern, central, and southwestern subprovinces by zones of 

large-scale strike-slip faulting across which no detailed lithostratigraphic correlations are possible (Cox and Briggs, 1973). Berryhill 

and others (1960, p. 142-143) proposed a general correlation of the 

Fajardo Formation in the northeastern subprovince with rocks of 

similar age in the central subprovince. Their correlation remains valid 

even though the Fajardo is now recognized to be Early Cretaceous 

rather than Late Cretaceous because the age assignment of the central subprovince rocks also has been changed (Briggs, 1969, p. 14). 

The Fajardo of probable Albian Age can be correlated with relative 

precision with the Albian Torrecilla Breccia (Briggs, 1969, p. 7-15). 

Similarly, the Tabonuco, Hato Puerco, Cambalache, and Canovanas 

Formations and the Martin Gonzalez Lava (table 1) (the sequence 

overlying the Fajardo in the northeastern subprovince) can be correlated generally with the Robles-Rio Orocovis sequence of Albian 

to Santonian Age in the central subprovince (Briggs, 1971, p. 1), and 

the Figuera Lava, beneath the Fajardo, can be correlated with as-yetunnamed pre-Torrecilla volcanic rocks of the central subprovince.
G10 CONTRIBUTIONS TO STRATIGRAPHY

At this time, no reasonably precise unit-for-unit correlations can 

be made between the Cretaceous of the northeastern subprovince and 

the Cretaceous of the southwestern subprovince.

REFERENCES CITED

American Commission on Stratigraphic Nomenclature, 1961, Code of Stratigraphic Nomenclature: Am. Assoc. Petroleum Geologists Bull., v. 45, no. 5, 

p. 645-665.

Berkey, C. P., 1915, Geological reconnaissance of Porto Rico: New York Acad. 

Sci. Annals, v. 26, p. 1-70.

Berryhill, H. L., Jr., 1965, Geology of the Ciales quadrangle, Puerto Rico: 

U.S. Geol. Survey Bull., 1184,116 p.

Berryhill, H. L., Jr., Briggs, R. P., and Glover, Lynn, 3d, 1960, Stratigraphy, 

sedimentation, and structure of Late Cretaceous rocks in eastern Puerto 

Rico Preliminary report: Am. Assoc. Petroleum Geologists Bull., v. 44, 

no. 2, p. 137-155.

Briggs, R. P., 1969, Changes in stratigraphic nomenclature in the Cretaceous 

System, east-central Puerto Rico: U.S. Geol. Survey Bull. 1274-0, 31 p.

Briggs, R. P., 1971, Geologic map of the Orocovis quadrangle, Puerto Rico: 

U.S. Geol. Survey Misc. Geol. Inv. Map 1-615.

Cox, D. P., and Briggs, R. P., 1973, Metallogenic map of Puerto Rico: U.S. 

Geol. Survey Misc. Geol. Inv. Map 1-721 (in press).

Glover, Lynn, 3d, 1961, Preliminary report on the geology of the Coamo quadrangle, Puerto Rico: U.S. Geol. Survey Misc. Geol. Inv. Map 1-335.

Ingram, R. L., 1954, Terminology for the thickness of stratification and parting 

units in sedimentary rocks: Geol. Soc. America Bull., v. 65, p. 937-938.

Kaye, C. A., 1959, Geology of the San Juan metropolitan area, Puerto Rico: 

U.S. Geol. Survey Prof. Paper 317-A, 48 p.

Meyerhoff, H. A., and Smith, I. F., 1931, The geology of the Fajardo district, 

Porto Rico: Sci. Survey Porto Rico and Virgin Islands, v. 2, pt. 3, p. 201-360.

Pease, M. H., Jr., 1968, Cretaceous and lower Tertiary stratigraphy of the 

Naranjito and Aguas Buenas quadrangles and adjacent areas, Puerto Rico: 

U.S. Geol. Survey Bull. 1253, 57 p.

Seiders, V. M., 1971, Cretaceous and lower Tertiary stratigraphy of the Gurabo 

and El Yunque quadrangles, Puerto Rico: U.S. Geol. Survey Bull. 1294-F, 

58 p.

U.S. GOVERNMENT PRINTING OFFICE: 1973 SIO OO1/34