2

Fairly good exposures of felspathic sandstone and quartz-
itic pebbles belonging to the formation are found in Rose
Valley, Pa. (near Ambler Station on the North Pennsylvania
Railroad); but no traces of organic remains were here found.

Two miles northeast of Conshohocken, Pa., there are con-
siderable exposures both of sandstone and gravel belonging to
the formation, and of plastic white and mottled clays repre-
senting its upper member. The clays are extensively, and
the sands somewhat less extensively worked; but organic re-
mains were not here observed.

There are many exposures of the Potomac sandstone and
gravel over the higher lands all the way from the Schuylkill
river to the Susquehanna, many of which are indicated upon
the geologic map of Chester and Delaware counties under the
name "Brinmawr Gravels." There is little hope of finding ver-
tebrate remains, or indeed any other fossils in these outcrops.

Exposures of the formation occur in the northwestern
part of Wilmington, Delaware.

3

Several exposures occur in the vicinity of Newark, Del., where they have been studied with some care by Prof. F.D. Chester, who would direct a collector to the most promising localities.

The formation is magnificently exposed all about the head of Chesapeake Bay in precipices from 10 to 100 feet in height, accessible only by water. None of the exposures at this point have yielded traces of animal remains, though a few plant impressions have been obtained.

Perhaps the most prominent exposures of the formation are those in the vicinity of Baltimore. The deposits in this locality have yielded abundant plant remains, I believe a few mollusca, and bones and teeth of several vertebrates including Astrodon Johnstonii, etc. Prof. Uhler of the Peabody Institute, Baltimore, is more familiar with localities than I, and would I am sure, be glad to direct a collector to the most promising points.

The formation extends, and everywhere forms the surface from Baltimore to Washington; but no fossils have been found between these points.

DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

WASHINGTON D. C., Oct. 27, 1887.

Dear Sir:

Your telegram reached me duly, and I am indebted to you for your warning. I will say nothing about Mr. Hatcher's work; will not make mention of the matter in monthly reports; and have already cautioned Mr. Hatcher against giving publicity to his work or its results.

I have been somewhat negligent in not sooner reporting Mr. Hatcher's arrival and the commencement of his work at the close of a short vacation. Thus far Mr. Hatcher's success has far exceeded my expectations, though I fear the locality at which he is now engaged is largely a representative one. You will I presume deal directly with Mr. Hatcher in disposing of the material collected by him; and it will probably be best for me to add to his collection the few vertebrate fossils which I have already obtained from the Potomac formation.

I remain, sir, with great respect,

Prof. O.C.Marsh,
Yale College,
New Haven, Conn.

DEPARTMENT OF THE INTERIOR

WASHINGTON D. C., Nov. 5, 1887.

My dear Sir:

I have just been looking over Mr. Hatcher's
collection which will go to you to-day.

The locality in which Mr. Hatcher has been at work has
long been a puzzle to me since, while the deposits are petro-
graphically undistinguishable from those characteristic of
the upper division of the Potomac, the fossils secured seem
decidedly newer. It is accordingly one of those cases in
which I have suspected that the deposits consist of Potomac
materials rearranged and redeposited in ravines excavated
within the Potomac during later Cretaceous or Eocene time.
I did not think it worth while that Mr. Hatcher should spend
much time in this locality, because of the uncertainty as to
the stratigraphic and genetic relations of the deposits at
this point to those which constitute the great body of the
Potomac formation; but the material was so abundant and ap-
parently so interesting that I have encouraged him to continue

O.C.M. #2.

his work there until to-day. Of course it is desirable to
learn something of the age of the paleontology of the beds
upon which Mr. Hatcher has been at work, whatever their age,
since it is by paleontology alone that they can be separated
from the Potomac proper. It would seem to me that Mr. Hat-
cher's material is sufficient for this purpose and that unless
you think it worth while to follow up the lead already opened
he had better go to exposures which are unquestionably Potomac
but in which the chances of finding animal remains are slight.

Might I beg you to give me a few words of opinion con-
cerning Mr. Hatcher's collection as soon as you look over it
in order that I can the better decide what investigations
are necessary in relation to it?

With great respect,

Prof. O.C.Marsh,

Yale College,

New Haven, Conn.

DEPARTMENT OF THE INTERIOR

WASHINGTON D. C. Nov. 21, 1987.

Dear Sir:

In response to your communication of the 17th inst
I beg to advise you that Mr. Hatcher has now been at work for
over a week upon certain identified Potomac deposits; without
success, I am sorry, though not surprised, to be compelled
to say. He will spend two or three more of the pleasant
days we are now enjoying in this vicinity, and then go to a
typical locality on the James river below Richmond which has
yielded abundant plant remains, and one well preserved fish
tail. That locality is as promising as any with which I am
acquainted, and if you care to participate in the search I
should be glad to join you and convey to you and Mr. Hatcher
such local information as I have been able to gain during a
trip through the region. I cannot, however, offer you much
encouragement; for, as Mr. Hatcher's experience of the past
week proves, that the most skilfull and thoroughly trained
collector can spend day after day on exposures of the forma-

O.C.M. #2.

tion in which the material is turned over by the hundred tons
by large numbers of workmen, without finding the slightest
trace of animal remains.

There is not I think serious cause for apprehension concerning Mr. Hatcher's health. The weather is now quite pleasant here, except during the occasional rainy days which of course keep him indoors; and the pleasant season will not close on the James river for several weeks. It is doubtful however whether he will consider it profitable to spend more than the present week on the formation.

Very truly yours,

Prof. O. C. Marsh,

Yale College,

New Haven, Conn.

DEPARTMENT OF THE INTERIOR

WASHINGTON D. C. Nov. 26, 1887.

My dear Sir:

I spent yesterday with Mr. Hatcher in examining the locality at which his last lot of bones was collected in order to satisfy myself whether or not the deposits are Potomac. As I anticipated, after seeing the material, the excavation while a typical iron-ore working from which the carbonate of iron characteristic of the upper division of the Potomac formation, is extracted in considerable quantity, exhibits a heavy deposit of the Columbia formation (which is early glacial in age, but which would have no doubt been referred to the Pliocene on the evidence of invertebrate fossils) overlying the iron-ore clays. Although the workmen declare that the bones come from the subjacent clays, I cannot help suspecting that they come from the superior deposit. Moreover, I suspect that the Potomac clays at this point have been rearranged during some pre-Columbia submergence, and, accordingly, that fossils found therein will not indicate the age of the Potomac. I desire to assure you, however, that no person

O.C.M. #2.

not thoroughly familiar with the various aspects of the for-
mation would be likely to entertain such a suspicion; in all
its principal characters the deposit is identical with that
of the Potomac in place; and it is wrought by the iron miners
just as is the genuine Potomac. Mr. Hatcher is certainly in
no way blaneworthy for his failure to correctly discriminate
the exceedingly puzzling deposits in which the bones were
found.

Mr. Hatcher arranged to send his last findings to you
last evening. If they contain anything of Mesozoic age he will
work the dump-heap in which bones are known to exist; otherwise
he will visit the plant-bearing localities already mentioned
on the James river early next week.

I desire to repeat my assurance that while Mr. Hatcher's
discoveries have been of less value than if the fossils had
come from the Potomac proper, they are still of high value
to me, and will throw much light upon the complex and obscure
post-Potomac history of this region.

With great respect,

Very truly yours,

DEPARTMENT OF THE INTERIOR

WASHINGTON D. C. Nov. 30, 1987.

My dear Sir:

I am in receipt of your communication and have
also just conferred with Mr. Hatcher; and I am exceedingly
gratified to learn that at last some of the bones collected
prove to be Mesozoic. Mr. Hatcher has so thoroughly worked
the deposits in this vicinity without finding any other prom-
ising lead that I think it will be well to continue operations
at Muirkirk. Accordingly I have directed him (with the au-
thority of the Director who has just returned) to go into the
now abandoned working with half a dozen miners and spend a
week or more in search for additional bones. Mr. Hatcher goes
to Muirkirk this morning for that purpose. The James river
locality can wait the completion of his studies here, since
the weather will not prevent collection there for a month or
more.

With great respect,

DEPARTMENT OF THE INTERIOR

WASHINGTON D. C. Jan. 4, 1888.

My dear Sir:

I have great pleasure in acknowledging receipt of
a separate copy of your notice of new genera of Dinosaurs from
the Potomac formation.

I have not seen Mr. Hatcher since my return, but shall
interview him during the day or tomorrow; and I think I can
assure you that he can be prevented from yielding to his
besetting sin and working himself to death in the clay beds.

With great respect,