COMPARISON WITH SIMILAR GLACIAL DEPOSITS 271 



tion, these last deposits seem to resemble the early ones of the San Juan 

 more than do the intermediate ones. It is possible that the intermediate 

 terraces in the San Juan, which have been attributed to erosion alone, 

 may correspond to the earlier glaciation in the Bighorns, but that in the 

 San Juan region actual glaciation was very feeble or altogether lacking. 

 At the time that observations were being made in the San Juan region 

 Capps and Lefhngwell * were examining the Pleistocene deposits of the 

 Arkansas valley in Colorado. Two definite epochs of glaciation are noted 

 by them, and, as in the Bighorns, the possibility of a still earlier one is 

 recognized, although here also satisfactory proof of this is lacking. The 

 deposits of the last stage are of essentially the same character as those of 

 the San Juan, with the exception that lateral moraines are perhaps more 

 prominent in the valleys of the Sawatch range tributary to the Arkansas. 

 The deposits of the older drift are characteristically weathered and of 

 patchy occurrence and are found higher than the younger drift and be- 

 yond the limits of the last ice. In addition to the strictly morainal de- 

 posits, two distinct gravel-covered terraces were observed. Both of these 

 terraces are in close relation to the moraines of the earlier and later 

 epochs, and in this correspond to the highest and lowest terraces of the 

 Uncompahgre valley. The authors have noted no intermediate terrace 

 levels between the upper and lower ones, but the older drift, whose char- 

 acter is still open to doubt, occurs at a yet higher elevation, and here 

 again it may be found to correspond in age to the deposits on Horsefly 

 peak of the San Juan region, and the intermediate levels of the San Juan 

 in turn correspond to the older drift levels of the Arkansas valley. 



Whether these suggested correlations prove to be true or not is more or 

 less immaterial in the present connection, the important point being that 

 at least two definite and distinct epochs of glaciation have been recognized 

 at a number of widely separated points in the Eocky Mountain province, 

 and that the interval which occurred between them was one of long dura- 

 tion and in which extensive erosion took place. 



A more systematic examination of the Pleistocene deposits of the San 

 Juan region than has been possible up to the present time would undoubt- 

 edly throw light on many points that are at present obscure in regard to 

 the relative age of the drift and its relation to the various terrace levels. 

 Direct evidence would also doubtless be obtained bearing on the nature 

 and cause of the intervals of active erosion which occurred between the 

 different advances of the ice. At present it is impossible to say to what 

 extent climatic conditions played a part during these periods of erosion. 

 That actual uplift occurred seem* certain, but the nature of the uplift is 



* Op. cit. 



