552 GEORGE R. MANSFIELD 
sorting.t Probably the littoral deposits of lakes would approach 
marine deposits in uniformity of size and arrangement of particles, 
but with the absence of tides it is doubtful if these characteristics 
would be in general so highly developed. 
Estuarine deposits are seen to consist in the main of mixtures of 
sand and clay, not very well assorted, but relatively fine. The matrices 
of crush-conglomerates would doubtless present much diversity in the 
size and shape, but not in the material, of their particles. Probably 
glacial deposits display the greatest variation in the character of the 
finer fragments that constitute their matrices. Fluviatile deposits 
may often approach them in heterogeneity of material and arrange- 
ment, and in angularity of individual particles. One minute distinc- 
tion may, however, be noticed. In the case of small fluviatile frag- 
ments, which are only slightly rounded, the attrition will probably 
be equally developed on all corners or edges. In the case of similar 
glacial fragments, as shown by the microscopic study of the Dwyka 
conglomerate, one edge or corner of a particle may be smoothed or 
rounded, while other corners or edges remain sharply angular. 
The evidence thus far collected goes to show that the pebbles of 
marine and lacustrine conglomerates tend to be well sorted and well 
rounded, though they may be subangular in proximity to their sources. 
Shrubsole, noting the way in which pebbles on a beach slip over each 
other with the recession of each wave, remarks: ‘The pebbles 
become as a rule symmetrical and lose all traces of angularity.’”? 
Estuarine pebbles tend to be but imperfectly sorted and rounded, and 
fluviatile pebbles may show all stages from confused heaps to well- 
stratified beds and from well-rounded forms to almost complete 
angularity. The difference between marine and fluviatile pebbles 
is thus expressed by Dutton: 
Attrition [in the fluviatile conglomerates of the high plateaus] is not ordi- 
narily extreme. In most cases it is enough to indicate that the fragments are 
really abraded, though with no great loss of substance. The stones of sub- 
aqueous conglomerates, on the contrary, are always much worn and rounded. 
Again, the sizes of the stones [in the fluviatile conglomerate] range from a fraction 
of a cubic inch to several cubic feet; in rare instances to more than 2 cubic yard.3 
t High Plateaus of Utah (Washington, UOSO); D220. 
2 Quarterly Journal of the Geological Society, Vol. LIX (1903), p. 315. 
3 LOG Cit., 3. 224. 
