353 



Many of the remains are more or less silicified, and in 

 some cases are opalized. In most cases, the structure is 

 excellently preserved, the fossil wood being so like the 

 modern that in many cases it is easily mistaken for a piece 

 of recently weathered wood. 



The vertebrate remains occur at a higher level, some 60 

 or 70 feet (18 or 21 m.) below the top of the bank. The 

 bed containing them, varies from a yellow clay or shale to 

 a fairly compact gray sandstone, and the state of preser- 

 vation differs with the material of the bed in which it is 

 found. Some excellently preserved specimens are found 

 in association with the concretionary iron beds, but in these 

 cases, it is almost impossible to separate the iron from the 

 bone. 



Owing to the fact that most of the exposures are on the 

 steep face of the cut bank, it is sometimes difficult to find 

 the complete set of bones in place. As the bank is eroded, 

 some of the bones become undermined and roll to the bottom 

 of the slope, where they lie until completely broken up by 

 exposure. By tracing these fragments up the bank, some 

 may be found projecting a few inches from the surface. 

 To extract them from this bed means that a large amount 

 of overburden has to be removed, or that the bones should 

 be taken out by "mining". 



Most of the specimens found here are reptilian, of the 

 order Dinosaurs [6 and 7], although farther down the 

 river there are reported remains of fishes and small mam- 

 mals. None of these have as yet been found in this region. 



The exact position of this fossil-bearing bed is often 

 difficult to determine, owing to the tendency of the bank to 

 break and slide to the lower levels. On these slips, erosion 

 is often more effective than on the undisturbed levels above, 

 so that, in some cases, the bone-bearing beds have been 

 exposed by the butte weathering down to its level. In 

 such cases, the task of collecting is comparatively easy. 



The slipping of the banks mentioned befo:e is in this 

 formation even more prevalent than in other regions where 

 clay forms the greater part of the subsoil. The tendency 

 to slip is increased by the presence of a varying amount of 

 "bentonite" disseminated through the whole formation, 

 and sometimes aggregated in beds of considerable thickness. 

 This material when moist, is very waxy or soapy, and when 

 given sufficient amount of water has a tendency to become 

 very gelatinous and to expand excessively. The presence of 



