Pernio-Carboniferous Ammonoids of the Glass Mountains \J 



formity brings the Hess formation in contact with the older and 

 strongly folded member of the Pennsylvanian called the Dimple for- 

 mation, or with somewhat younger beds, equally much-folded and be- 

 longing to the Pennsylvanian, called Raymond formation by Baker,^ 

 or still other strata. This shows that the unconformity discovered by 

 Udden is of great importance for the local geological history but that 

 it does not constitute the boundary line between the Upper Pennsyl- 

 vanian and the Permo-Carboniferous. 



This is not the place for the discussion of the geological and strati- 

 graphical conditions of the Glass Mountains, which have been de- 

 scribed by Dr. Udden in a separate publication,^ but it is necessary to 

 explain the stratigraphical local names introduced by us, so that we 

 may be able to use them in the following text. 



DISTRIBUTION OF THE AMMONOIDS IN THE DIFFERENT FORMATIONS 



The upper formations — the Tessey, Gilliam and Vidrio dolomites — 

 do not seem to be very fossiliferous and no cephalopods have been 

 found in them at the places where I could study them. 



Our ammonoids have been found only in the lower part of our Per- 

 mo-Carboniferous : in the Word, Leonard, Hess and Wolfcamp for- 

 mations. The richest in genera and species are the highest and lowest 

 of these — the Word and Wolfcamp formations; while the Leonard 

 formation is extremely rich in specimens which belong to few genera 

 and species. The Hess formation has given only two species up to 

 this time; one of which is even not entirely without doubt as to its 

 age; but the Hess formation has been less studied than any of the 

 other divisions and there is the possibility that richer localities may 

 yet be found. The species of our fauna are distributed in the different 

 formations in the following manner : 



Wolfcamp formation: 



Daraelites texanus, n. sp. 

 Uddenites Schueherti, n. g. n. sp. 

 Uddenites minor, n. sp. 

 Gastrioceras modestum, n. sp. 

 Schistoceras diversecostatum, n. sp. 



'Cf. Udden, Baker and Bose, Review of the Geology of Texas, p. 46. 

 'University of Texas Bulletin, No. 1753. 



