206 J. Mar coa — Jura and Neocomian of Arkansas, 



that the A. Shumardi does not exist anywhere at Pyramid 

 Mount ; therefore its stratigraphic position in the Tucumcari 

 region must be above the last bed of white limestone, seen at 

 the top of Pyramid Mount. This remark is of great impor- 

 tance, for Professor A. Hyatt, in his exploration of another 

 part of the Tucumcari region, insists that he has found the A. 

 Shumardi in company with Gryphcea Tucumearii. However 

 great may be my respect and sympathy for Professor Hyatt, 

 and though I fully acknowledge his great authority on cephal- 

 opods, regarding him as one of the few masters on everything 

 touching Ammonites, Nautilus, Lituites, etc., I cannot refrain 

 from expressing my doubt in regard to his findings!. Shumardi 

 is the same layer, side by side with G. Tucumearii. That 

 Professor Hyatt saw the Ammonites very near the Gryphcea, 

 I have no doubt ; but I am sure the Ammonite must be above, 

 even if only a few inches separate them. If the G. Tucumearii 

 exists above the A. Shumardi, and this is a well established 

 fact, which can be easily proved by a careful and exact strati- 

 graphist ; then A. Shumardi, as I have said, is a Jurassic 

 species, notwithstanding that it belongs to the genus Schlcen- 

 hachia, which in that case made its appearance in America 

 earlier than in Europe.* 



That beds found -at other parts of the Tucumcari region, 

 lying above the two feet of white limestone of the top of 

 Pyramid Mount, belong to the Lower Cretaceous or Neoco- 

 mian is very probable, but I am not to be criticised for not find- 

 ing them, for they do not occur at my section of Pyramid 

 Mount. I found there only the Jura and I followed all the 

 rules of stratigraphic classification, in referring the strata of 

 Pyramid Mount to the American Jurassic formation. I saw 

 clearly when I was on the top of Pyramid Mount, that on the 

 mesa or plateau of the Llano Estacado, more especially toward 

 the east, at Monte Pevuelto, there was another series of 

 strata capping the Jura of Pyramid Mount and consequently 



* In my paper, "The Jura of Texas" (Proceed. Boston Soc. Nat. Hist., vol. 

 2*7, p. 155), I say that Professor A. Hyatt has found at the Tucumcari region 

 the Ammonites (Schlcenbachia) Shumardi with the Gryph&a Tucumearii, " and 

 there is therefore no doubt possible in regard to the contemporaneity of the A. 

 Shumardi and the G. Tucumearii." Messrs. Dumble and Cummins in their Kent 

 section (American Geologist, vol. xii, 1893, pp. 309-314), also regard the A. 

 Shumardi as contemporary with the G. Tucumearii. Although I was not con- 

 vinced by the assertion of Messrs. Hyatt, Dumble and Cummins, I admitted it, 

 leaving the responsibility on those observers. But now, after the repeated fail- 

 ure of my adversaries to give the exact position in the strata of each species, I 

 am unwilling to accept any longer such supposed contemporaneity, and I think 

 that Ammonites Shumardi is younger than Gryphcea Tucumearii and is placed 

 above it in the strata ; and that the line of separation between the Jura and the 

 Neocomian at the Tucumcari region and at Kent, is between the beds containing 

 the G. Tucumearii and those above containing the A. Shumardi, with a break or 

 discordance of some sort between them. 



