CHARACTERISTICS OF TYPES OF CONGLOMERATES 555 
structure, irregular and striated pebbles, while furnishing strong evi- 
dence of glacial action, cannot be considered as conclusive proof, for 
such structures and forms may be produced in other ways. When, 
however, such forms are found to rest upon a smoothly polished and 
striated rock surface, the weight of evidence is so great that no other 
explanation can be accepted. 
To summarize:, Marine sediments exhibit, on the whole, the 
greatest uniformity of composition and the most orderly arrangement 
of materials, while glacial deposits display the opposite characteristics. 
Lacustrine, estuarine, and fluviatile accumulations attain intermediate 
degrees of uniformity. Each of the various types of conglomerate 
possesses features that are shared to some extent by other types. 
Thus there is no single feature which in itself distinguishes any partic- 
ular kind of conglomerate. It is only when a number of features of 
one type are grouped and compared with a similar group of another 
type that definite distinctions can be made. Such a comparison is 
attempted in the accompanying tabular summary. 
