290 



LEWIS G. WESTGATE 



beneath the blow of a" hammer, while the same rock on the inside of 

 the younger moraine is quite fresh. It may be noted, though, in this 

 connection, that in one or two exceptional cases the younger moraine 

 contains frequent decomposed bowlders. 



It is, however, when we come to examine the gravels associated 

 with the two moraines that the difference in amount of weathering 

 is most apparent, and numerous placer openings and trial shafts in 

 the gravels have made this comparison easy. Sections in the gravels 

 in the gorge show that the bowlders are, with very few exceptions, 

 perfectly sound. Numerous sections in the upper gravels show a 

 large proportion of the bowlders to be thoroughly rotten. One of 

 the most easily recognized rocks of the region is a coarse porphyritic 

 granite. In the gorge gravels, bowlders of this rock are fresh. In 

 the upper terraces they can often be picked apart with the knife-blade, 

 and frequently have been cut across in digging the shaft, it being 

 easier to cut across than to dig out blocks lying in the wall of the shaft. 

 This very general and thorough weathering of the upper gravels,, 

 compared with the freshness of the gorge gravels, indicates that the 

 former are several times older than the latter, and that interglacial 

 was longer than postglacial time. 



C. Differences in topographic expression and in amount of 

 stream-dissection of the two moraines and their associated gravels. 

 In a later place this consideration will be presented more fully. It is- 

 enough here to say that the younger moraine is the steeper and more 

 rugged of the two. The differing amount of dissection is especially 

 well brought out in the two gravels. Of course, the gorge gravels 

 have been in large part cleaned out by the Arkansas in postglacial 

 time, since along the main river conditions have favored erosion. 

 More striking is the great amount of destruction of the upper gravels- 

 at points where erosion has not been favored. They have been 

 completely cleared away by Lake Creek at its mouth, and by the 

 small stream entering the Arkansas at Hayden. Between these 

 two points no permanent streams enter the Arkansas from the west,, 

 but several dry valleys head in the old moraine, cross the wash-plain 

 and enter the main river. Near the river they are in granite and 

 narrow, farther back they are in gravel and widely open. These 

 widely open valleys in the old gravels contrast well with valleys cut 



