24 Field Museum of Natural History — Geology, Vol. IV. 



vation of any mammalian fauna which may have found its way into the 

 Uintah basin at this stage. 



Fossils in the Upper Metarhinus Zone are found almost without 

 exception in the sandstone ledges, rarely in the shales which alternate 

 with them. Sometimes they occur in the homogeneous, fine-grained 

 sandstone but more often they are confined to the narrow, coarse- 

 grained, cross-bedded layers which often occur near the base, sometimes 

 at the top, of massive ledges. Skulls are often embedded in semi- 

 gravelly layers and have their narial or orbital cavities filled with 

 pebbles which could be carried only by rapidly flowing water. Another 

 evidence of stream action lies in the complete dissociation of the various 

 skeletal elements. Seldom are the lower jaws associated with the 

 skulls, or so much as two vertebras found articulated. There are ex- 

 ceptional instances where whole skeletons are found but little disturbed. 

 In the few instances noted these were embedded in a fine-grained, 

 homogeneous sandstone apparently deposited in more quiet water such 

 as deep pools or eddies. 



The Upper Metarhinus Zone presents a much more varied fauna. 

 It includes, along with the low-ground titanotheres, a number of forms 

 whose structure indicates greater activity and which may have inhabited 

 woodlands or open plains. Throughout this series there appears an 

 ever-increasing percentage of upland forms. The titanothere genera 

 Metarhinus and Dolichorhinus are equally well represented. Their 

 fossil remains are usually found associated in the same ledges and 

 apparently deposited under the same conditions. In the one instance 

 in which a large part of a Dolichorhinus skeleton was found articulated, 

 a skeleton of a young Metarhinus was mingled with it in such a manner 

 that it was at first mistaken for the young of the same form. There 

 is one notable exception to the parallel occurrence of these two forms 

 in the Upper Metarhinus Zone. An isolated ledge of sandstone repre- 

 sented at the base of Section 2 (Fig. 2) yielded Metarhinus skulls 

 and jaws in relative abundance. Four specimens of M. riparius 

 and three of M . earlei are recorded from this ledge but no trace of 

 Dolichorhinus was found in it. It is significant that such titanotheres 

 as Telmatherium and Mesatirhinus superior also occur in this ledge. 

 It was noted also that Dolichorhinus was found only in heavy sandstone 

 systems. Apparently this animal was confined to the vicinity of large 

 streams. 



Other genera common to the Upper Metarhinus Zone are the more 

 rare and probably upland Rhadinorhinus , the gigantic Eobasileus, the 

 small hyracodont Triplopus, and two large creodonts, Mesonyx and 

 Harpagalestes. Occasional crocodiles and numerous turtles are found, 





