20 University of Texas Bulletin 



At the present time it is difficult to decide how near the relationship 

 is between the zone of Uddenites and that of Prothalassoceras, because 

 so few ammonoids have been found in the latter one. According to my 

 provisional observation also the brachiopods and gastropods of these 

 two zones have more affinities with the Pennsylvanian than those from 

 the two upper zones, although in the zone of Perrinites occur somel 

 gastropods of entirely carboniferous aspect. 



We have to take into account also that we do not know how much 

 material of the zone of Uddenites was removed by erosion before the 

 zone of Prothalassoceras was deposited. Near the Wolf Camp the con- 

 glomerate is about 45 feet thick and indicates considerable erosion; 

 therefore quite a number of beds may be unknown to us because they 

 have been carried away and are not preserved anywhere else in this 

 region. 



Thus we arrive at the following conclusions: There is a certain 

 affinity between the zones of Waagenoceras and of Perrinites, while 

 the ammonoids of the two lower zones show a distinct and somewhat 

 older character; the degree of relationship between these two latter 

 zones cannot be exactly determined, on account of the scarcity of am- 

 monoids in the upper one and because we do not know how much mater- 

 ial has been destroyed during the erosional period which separates the 

 zones from each other. 



We have already mentioned that the dolomites on top of the Word 

 formation do not seem to be very fossiliferous and that an exact de- 

 termination of their age cannot be made; the fossils only show that 

 these bed? belong still to the Permian, but it is impossible to say where 

 the Permo-Carboniferous ends. 



Soinewhat different are the conditions below our fossiliferous series. 

 The shales and limestones which carry the ammonoids of the Wolf- 

 camp formation rest on the very characteristic gray limestone which 

 may be followed to the east as far as Gap Tank. This limestone con- 

 tains a small fauna of brachiopods, pelecypods, gastropods, etc., of 

 decidedly Pennsylvanian character. At Gap Tank the rocks underly- 

 ing the afore-mentioned limestone are well developed ; they consist of 

 shales alternating with rather thick-bedded whitish-gray limestones 

 similar to the upper one, and farther below of sandstones, limestones, 

 shales and several conglomerates. In the continuation of this series 



