( Copy. )

( Personal. )

New Haven, Conn.,

March 18, 1889.

Dear Mr. Cross,

I did not know until Saturday, when Professor Dana gave me the proof of your article, that you were ready to use officially the fossils from the Denver region as direct evidence of the age of your new formations. I was somewhat surprised, therefore, to find that our informal conversations were quoted indirectly as my opinions on the subject, and in connection with some facts quite new to me. I would have sent a written statement had I known it was needed, but I was waiting for the new fossils that Mr. Emmons promised me in January last, before summing up the evidence. This will explain my telegram of Saturday, the answer to which came to-day.

It is too late now to make more than a few verbal changes in your article, and I will send with this, proofs of the pages on which these corrections are suggested. Please telegraph me on receipt of this, if you wish them made or not. I think it much

better to have them made now in your article than elsewhere.

Let me say in a word (1) that of all the fossils from the Denver region, submitted to me, I understood that only three or four were found in place, the others being surface specimens, (2) that all these specimens, with the exception of three or four still in doubt, point clearly to the Laramie formation as their probable source, and not to the Tertiary.

I hope Mr. Cannon's fossils will soon be here, and then we will have more light on the subject.

( Personal.)

New Haven, Conn.,

March 20, 1889.

Dear Mr. Cross,

Your letter with proof came this morning. The
corrections were soon made in the form you wished, and the article,
believe
is now printed.
I see by both your letters that we do not quite
understand each other, and I hope soon to talk the matter over
with you.
If we could have done so here, with the specimens
before us, I think most of the difficulites that trouble you so
much about the age of the Denver beds could have been removed.

You have made an admirable presentation of the stratigraphy
and lithology, but I cannot agree with your paleontology.

Hoping the fossils you send to-day will help us out,

O. C. Marsh.

DEPARTMENT OF THE INTERIOR

UNITED STATES GEOLOGICAL SURVEY

WASHINGTON, D. C.

Feb. 13, 1892.

Prof. O. C. Marsh,

New Haven, Conn.

Dear Prof. Marsh:

In talking with you at New Haven the other day I understood you to say that the Puerco group of Cope was simply a part of the Wasatch. I have been examining, since my return, the revision of the vertebrate fauna of the Puerco, by Cope, in 1888, and I find that his summary of that fauna seems to distinguish it very markedly from what he calls the Wasatch. I should like to ask you therefore on what grounds you can consider the Puerco as identical with the Wasatch? Cope's statement, if I read him correctly, is that out of over 100 species of fossil vertebrates found in the Puerco not one came to it from the Laramie and not one survived into what he calls the Wasatch. He also mentions a considerable number of Marsupials with very strong Mesozoic affinities. Now is his statement as to the distinctness of the Puerco fauna incorrect, or do you distinguish an upper and lower Wasatch, whose faunas are specifically distinct? I confess I am a little puzzled by this disagreement as to the position of the Puerco.

Do you object to my stating, in the article I am now preparing, as
upon your verbal authority, that none of the formations you have
been describing from the Ceratops beds, whether the reptilian or
mammalian, have actually been found in the Laramie of the well-
known localities along the U. P. Railroad in southern Wyoming?
Do you regard the "Agathaumas" of Cope as definitely belonging to
the Ceratopsidae?

DEPARTMENT OF THE INTERIOR

DIVISION OF VERTEBRATE PALEONTOLOGY

NEW HAVEN, CONN.

February 17, 1892.

Dear Sir:

Your note of the 13th inst. came duly, and I reply in my first moment of leisure, as you seem to have misunderstood me on several points. If you will look at my article in the Journal of Science for January, you will see that I certainly consider *Agathaumas* as belonging to the *Ceratopsidae*. Moreover, I know of several other specimens that have actually been found in the Laramie along the U. P. R. R. in southern Wyoming," or in that vicinity.

Again, about the Wahsatch, you certainly misunderstood me. I have spent a good deal of time on this formation, and have one of the largest collections ever made in it. It is all Lower Eocene, which I call the Upper and Lower Conyphodon beds, or Upper and Lower Wahsatch, if you prefer. The so-called Puerco beds are Lower Wahsatch.

I will send you in a few days an article on another subject, which I discuss this matter, and I hope you will find a number of your questions answered in it. You may quote from this all you please, but I rather not be quoted verbally unless you send me your quotation for approval.

Yours, very truly,

DEPARTMENT OF THE INTERIOR

WASHINGTON, D. C.

Feb. 27, 1892.

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

Dear Prof. Marsh:

Your reply to my note came duly to hand and I thank you
for it. A few other little questions have arisen which I should
like to trouble you with, as I do not know of any other way to get the
desired information.

I have just found by accident that Prof. Leidy described in
Volume 7 of the Hayden monographs, page 267, a Dinosaur, Poicilo-
pleuron, which was found in Middle Park, Colorado, according to the
statement of Hayden. Can you tell from Leidy's description any-
thing of the affinities of this animal, of which he had only one
vertebra? Is there anything to indicate that it is related to the
Ceratopsidae, or does it belong to older formations? Does it
correspond to forms known in the Laramie more nearly than to those
from the Dakota or Jura?

I should like very much also to obtain a list of the genera,
or at least of the families which are represented in our collection
from the Denver region. This is primarily for my own information,

2

and will not be published unless you are entirely willing, of course. I am particularly anxious to know if you obtained from the Arapahoe or Denver beds any representatives of the mammalia. Eldridge thinks that he did find some teeth at least, which you referred to mammals, and if so they might possibly be identical with some of the species you have described further north.

I should like very much to get a list of the Dinosaurs known to occur in the Laramie proper, that is the coal-bearing Laramie, especially of Colorado and adjacent territory. I find that most of the descriptions of most of the described species come from illdefined localities, and if there is any list where I can possibly get this information, would you kindly give me the reference.

We are trying to make a final arrangement of the Denver man-
uscript, and I hope that your material for the chapter on verte-
brates is well under way.

( Copy )

DEPARTMENT OF THE INTERIOR

NEW HAVEN, CONN., March 30, 1892.

Dear Mr. Cross,

Your note of February 27th was duly received, but I
have not been able to reply until now. Moreover, the questions you ask in-
volve answers requiring a good deal of work which I cannot give to the sub-
ject at present. Some points are easily settled, and those I am glad to
answer.

Leidy's *Polcilloleuron* is based on half a vertebra, but this is charac-
teristic for the order at least. It is allied to *Megalosaurus*, and has
nothing to do with the *Ceratopsidae*. It might have come from the Jura,
possibly from the Laramie, and was certainly Mesozoic.

You ask if I have obtained from the Arapahoe or Denver beds any Manna-
lia, and say that Eldridge thinks he found some teeth which I referred to
mammals. In this he is certainly mistaken, as I have never seen a mammal tooth
from either of those beds. Had it not been for that snow storm two years
ago last November, I am sure Hatcher would have found mammals in the vicinity of Denver.

I have no list of the Dinosaurs from what you call the Laramie proper,
of the coal bearing Laranle of Colorado and adjacent territory. So far as
I remember them, they are of the same types as those in the Ceratops beds,
but a careful comparison may show some of them to be distinct. There are
coal seams in the Ceratops beds, and *Ceratopsidae* in the coal beds, and the
great break is not between them, but above both, so far as I know, at
*Jeromitomorpha*.

( Copy )

New Haven, Conn., August 18, 1892.

Dear Mr. Cross, -

I duly received your note in reply to mine con-
taining an extract from Hatcher. You do him injustice in speaking of him
as a collector, and not as a geologist, and you will make a great mistake if
you undervalue his knowledge of the Laranie, of which formation he has proba-
bly seen more than any other man. In a recent letter, he informs me that
the Ceratops beds have been traced by him <u>underneath</u> one of the great pro-
ductive coal mines of eastern Wyoming. I state this to you now confidential-
ly, <u>and</u> not to be quoted, as we shall publish this and other important
points relating to the Laranie as soon as the present investigation is com-
pleted.

You said nothing in your letter about having Cannon send on to New
Haven his vertebrate fossils from near Denver. It is more important to have
these now than ever before, if you wish to know the relations of your Denver
beds to the other horizons rich in vertebrate remains.

DEPARTMENT OF THE INTERIOR

WASHINGTON, D. C., March 2, 1894.

Prof. O. C. Marsh,

New Haven, Conn.

My dear Prof. Marsh:

In preparing my description of the Pike's Peak district, to accompany my map of the region, which is to be published this spring, I come to the question of fossils obtained from the Jurassic of the Oil Creek section. As to the vertebrates I know that you have published a great many descriptions of material stated to come from this locality, but I presume you know of a good many other species as yet undescribed, and probably have described a number from this locality without definite statement of that fact. Would it be agreeable to you to furnish me with a list of the vertebrates known to you to occur in the Jurassic of the Oil Creek section? If not a complete list, a list of the published species. I have consulted Dr. White's bulletin on the invertebrates of the fresh water Jura, in which he describes a number of species occurring in the Dinosaur beds of Oil Creek, and also refers to your collections of invertebrate fossils from the same locality. Has any of your material been described or identified in any form that I could use in my bulletin?