Evening star. [volume] (Washington, D.C.) 1854-1972, 1885-07-11

ren, esented also by the isolated butte just east
- bem nts bridge, upon which old FIT. Mahan
is aoctAteu. Both Of these terraces are carved
GUY o! me deposits of the Potomac formation.
mus tar 1t has been found impossible to cor
east side of the Potomac with those upon the
WSst, the probable error In determination of
a S;s. "eing OF greater value than the vert
cal distances separating the different terraces
the deposits Of the Columbia formation is har-
monious; The obvious genesis of the Washing
ton brickclays and gravels indicates that at
period probably as recent as late Quaternary
the mes, sea occupied the broad basin in which
washington Is located. The rock terrace skirt
| ing the north shore of the Potomac from George
town to Great Falls was manifestly formed
corrading its channel The phenomena of the
great terrace plain extending nearly from Fort
Myer to Falls Church indicates that at a period
| so recent that subsequent erosion has not yet
extended itself over the entire plain and at
mospheric decay has but little affected it's
| surface, the ocean waves swept along shore
200 feet higher than that of to-day. The higher
terraces of Tenallytown and elsewhere suggest
feet above its present limits at date SO recent
that beach marks yet remain upon the hills
rnas IN the most recent period OF the geologic cal
the highest lands of the District; and there is
induoltable evidence that the elevation of the
lana so recently Initiated Is yet in progress.
THE LITHoLOGY AND MINERALOGY OF THE
DISTRICT.
The rocks Of the District have been studied by
Mr.. George P. Merrill, of the National museum
and the minerals by Mr.. Merrill and Prof. F. W.
Clarke, of the United States geological survey.
The former gentleman has contributed the fol.
lowing lists part of the results of his studies:
the prevailing rocks of the District are mics.
smaller Quantities occur n soanstpne 3mass, va
steatlte) and epidosite-the latter evidently 8
vein formation.
very rarely in small fiakes), pyrite, lamellar
menaccanite, magnetic, rutile, quartz lboth
massive mass and chalcedonic but very rarely in
vite, aibite, black tourmaline, sphene, laumon-
title, stilbite, heuandite. prochlorIte. apatite.
vivianite and calcite. OF these the magnetic
microscopic crystals, while the garnets and
epodlte occur in such forms to be of interest
only to the local collector Up to date only the la
mellar menaccanite. rutile, sphene, prochiorite,
laumontite, heulandite and calcite have been
found In such form Us to be Of interest to gene
raj collectors
These rocks and minerals are on exhibition
In the National museum.
1t should be mentioned that the rocks in the
foregoing list occur within the formation here
denominated the Washington gneiss and that
with the exception of vivianite the minerals
secting it. The vivianite together with
Ignite and carbonate of iron, occur in the
bonaceous stratum intercalated between the
Columbia and Potomac formations: while lig-
mite and beautiful specimens of silcified wood
occur in the lower of these formations.
IL should be mentioned also that mica occurs
"a VIZ WINS ihtSiSCStihS Tue eutISSlC LOuc Ira
versing the western part of the District; and
while crystals of such size as to yield merchant
able plates have not yet been found within the
District, valuable mica has been extracted in
Montgomery county, Md, a few miles to the
northward. Gold has also been found in very
small quantities in quartz veins toward the
western margin of the gnessic zone. and in
other localities in Maryland; and similar dis
coveries TN the veins within the District would
not be astonishing to the mineralogist. There
is not, however, the faintest probability that
gold or other precious metals viii! ever be found
within the District in paying quantities.
The carbonate Of iron already noted as occur
ring about the summit of the Potomac forma-
ton in the northern part of the District and
contiguous portions OF Maryland is of some
economic value, but there is no probability
that it will ever be found in such quantities us
TO warrant investment of capital in extracting
Apropos to the reported discovery of petro-
ieun IN the city a few weeks ago, 1t may he
added that the only horizon at which accumu-
lation of hydrocarbons is possible is the carbo-
naceous stratum beneath the Columbia grav~ls
and sands, and that it is useless to look for
considerable quantities of petroleum other
hydrocarbons at this horizon for gold in the
quartz veins in the western pant OF the District