The daily morning journal and courier., 1907-04-25
ROCKS UNDER NEW YORK
PROF HOVETMAKES PLAIN THE
 GEOLOGY OF THE CITY.
Specimens of Rock from $50 Feet Down-science Helped by Subway and skyscraper Building-Radium Among the Minerals Found.

ing around Manhattan Island, know anything about the formation of the
 bed rock of this great city? A very few, probably, and yet at the Museum of Natural History there are two col
 " ctions that tell the story.
 Specimens of the rocks on which Manhattan Island rests are exhibited at the north end of the Hall of Geology and an almost complete collection or the minerals to be found on the island is on exhibition in the Morgan Mineral hall. This collection is the property of the New York Mineralobical club and is lent to the museum. In addition there are collections of rocks taken from the subway excavations, and from the foundations of large buildings ill various parts of the city.
 Recently some interesting specimens that came from a distance of $50 feet below the surface have been added, | and Dr. Edmund Otis HoVey, who has charge of the collections, hopes soon 10 get specimens from 650 feet below the ground It is possible to get these | specimens because of the plunger type of elevator now used in most of the 1 big buildings.
 The elevator is raised and lowered on a plunger that works in socket, | which of necessity must be as deep as l the extreme height to which the ele- vator is raised. In boring for this | socket drill which cuts hole about | twelve inches in diameter is used,and | the rock comes out of the ground in a solid core about ten inches 1T. diameter and usually ten or fifteen feet long. | These sections are excellent examples 1 of the bed rock
 Dr. Hovey has been at the collection now for something like five years and | while t Is almost complete he finds l something new now and then. Tine | collection of rocks is particularly in- l teresting to contractors and engineers. | and there is a chart that will show | just about what may be expected in | all parts of town.
 "The foundation of Manhattan Is- | land consists entirely of chrystalline rocks, gneiss, mica, schist, hornblende | limestone or dolomite," said Dr. Hovey | the other day Cutting through the 1 gnelss and schist there are countless l veins and dfkes of granite and pegma- | tite, and these have supplied most of 1 the minerals for which the island is noted.
 'The chrystalline rocks have been l covered with Q mantle Of glacial drift -unstratifed gravel, sand and clay of varying thickness-while below Four l teenth street there are extensive river 1 dposlts of stratl1ed gravel, sand and | clay among bosses of rock Cschist), i most of which were below the ancient
 water level
 "The major portion of the island consists of Gneiss and schists, the gem | eral trend or strike as geologists call 1t, of which. is north, northeast south and southwest These rocks are to be
 found in almost every excavation for
 building purposes, and there are many | excellent exposures of them, which
 fortunately will never be covered in
 Central park, Riverside and Morning | side parks, and along the Speedway
 and Lafayette boulevard.
 "The area of serpentie is very small ! a., tr ar, ffralx 1R hn-
 cause of buildings, Oneflocation is at
 Tenth avenue and West Fifty eighth
 street, The magnetism limestone ol
 dolomite, occurs in zones in Harlem
 where 1t is now almost covered with
 buildings and in the Kiagsbridge sec.
 tion of the island, where a good ex. posture may be seen along the Spuy'
 ten Duyvil ship canal
 The mica schists andA gneisses arc
 now considered by geologists to bt shades of Hudson river (lower sluriar
 age) which has been altered to theil
 present chrystalline condition by hea' and pressure combined With motion
 The chrystalline limestone, which I:
 almost a marble in some beds, is mncl older, geological1y speaking. It's pres. ent condition is due to the severe
 metamorphism, which 1t has undergone
 in company withthe schists
 "The hornblende schists are consid- cred to be of igneous origin, whicl would lnq1cate that VHlsA fcSlon eNpefl enced volcanic activity. millions O , years ago. These schsts occur in com - paratively small detached areas, ant ! are the highly metamorphosed repre-
 sentatives of the motion lava whicl was forced Into the cracks in the olt z sedimentaries and solidifled in the form
 of trap dikes, or was poured out oi
 the ancient surface in sheets, Th' hornblende schist may be distinguish ' ed from the incloslng mica schist b, , it's darker color, due to the abundance of dark hornblende
 , "Actinolite and tremolite schlsts oc | cur in company with some of tn i hornblende schists. East of the liar lem river and north of Spuyten Duty VII Creek thereis gneiss resembling 5 some of the Manhattan Island gneis | in appearance, which is older thai
 that and antedates even the magnesiai [ l limestone.
 "The minerals of Manhattan are fo the most part silicates of comple. chemical composition, and they var : with the nature of the rock with whicl f they are associated. It is comparative
 ly easy, therefore, to group them ae l cording to their occurrence into tn 5 minerals of the gneisses and the gran ite and pegmatite veins and dikes, tn
 ! limestone beds and the serpentine are and this subdivision has been followe l in the arrangement of the collection.
 The minerals of the gpeisSes an
 1 schists are primarily quartz, feldspa and mica, the last predominatng. | ths association the minerals rarely oC
 cur upon Manhattan Island as hand
 some cabnet specimens. But there oc cur with them, as secnodary effects O the metamorphism of the original bed
 fibrolite, epidote and other species
 Crevices in the schists have give opportunity for the formation fror I circulating waters of interesting littl , globules of spherosderite and severa members of the group of zeolites. Tn stilbite occurs in noteworthy rosette v of slender bladelike yellowish brow
 lcrystals upon the surface of the rock
 iThese zeolites are particularly inter ! l esting for study in comparison wit the remarkable specimens of the sam f 1 species which have come from the cav ' | tiles in the trap rock in the neighbor l ing palisades.
 5 'The chief cabinet mineral of tn | hornblende sehists Is sphene, whie P occurs in showy groups of yellowis green, hattened crystals. The princi pal constituents of the schists, how . ever is black hornblende, which oC
 CUTS in needlelike crystals.
 Q "Epdote too, and actinolite are oft en found in this rock, Exposure s may be seen in Morningside park an $ the Fort Washington Heights sectiol ;. but in most other localities it has bee covered by buildings or streets s "The granite and pegmatite views c f dilSes are the principal contributors = the local mineral collection. The or I igin of these rocks are still moote n point, but probably some of them ar I acid igneous intrusions, while other particularly the pegmatites, which al = characterized bytheir coaseness = specialization, are the result of chen
 ical precipitation from circulating wf
 ters. First to be mentioned are orthC . clase, microline, oglioclase, and albit e biotite among the micas and quartz. "Garnets of small size are scattere
 all through the schists, but gigant . crystals of this mineral have bee l. found in the pegmatite veins, u