PENNSYLVANIAN-PERMIAN GLACIATION 471 



Pennsylvanian conglomerates, however, is such as to indicate their 

 fairly constant association with water, as shown by the presence of 

 many rounded water-worn pebbles and boulders, and their deposi- 

 tion in fairly distinct coarsely stratified beds. Furthermore, the 

 Pennsylvanian conglomerates are not associated with any deposits 

 suggestive of arid or desert conditions, such as the salt and gypsum 

 deposits formed in later Permian time, but are on the other hand 

 associated with coal seams and dark-colored carbonaceous shales 

 indicating a relatively humid climate such as is required for abun- 

 dant vegetation. 



3. The great thickness of single conglomerate beds repeated at 

 intervals in a series, is another striking feature. In the section at 

 Franks there are at least five distinct conglomerate beds or forma- 

 tions, each ranging in thickness from 1 50 to 3 50 feet. In the section 

 along Honey Creek, near Davis, the conglomerate is between 200 

 and 300 feet thick. There are other places where the thickness may 

 reach as much as 1,000 feet or more. Such great thicknesses of 

 conglomerate, it is believed, are rarely if ever formed upon the shores 

 of ancient or present seas under ordinary conditions. On the other 

 hand, such thicknesses of raw, unweathered debris are the common 

 characteristics of conglomerates formed upon land, or in adjacent 

 sea bottoms where glacial conditions exist, or have prevailed in the 

 past. 



4. In addition to the above-described characteristics which are 

 usual features of glacial formations, there are the phenomena of 

 striation and grooving which are believed to furnish the distinctive 

 evidence of glacial action. 



It may be thought by some that the strice about to be described 

 and illustrated by these specimens may have been formed by some 

 other means than glaciation, such as by artificial means, or by such 

 rock pressure movements as are developed along joint planes and 

 fissures, in the manner of slickensided surfaces. There are, of course, 

 various kinds of marks to be observed on rocks, both artificial and 

 natural, and it seems hardly necessary to state that these various 

 phenomena have been considered in the search for evidence of the 

 glacial origin of these conglomerates. There are, for instance, 

 numerous examples of polished and grooved surfaces developed 



