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MANSFIELD: ROXBURY CONGLOMERATE. 255 
deposits of India coarser sediments tend to encroach upon and to 
overlie the finer materials near the mountains. 
It may be questioned whether fluviatile agencies are able to accu- 
mulate so great a thickness of sediments as that known to occur in the 
Narragansett Basin, and especially so great a bulk of fine silts and 
sands as that indicated by the Somerville and Cambridge slates. 
In reply the case of the Siwalik group of India noted on page 111 may 
be cited. This group, assigned to fluviatile origin, attains a thickness 
in the northwest Punjab estimated at 14,000 feet. As regards the 
second phase of the question it has been shown (page 112) that the 
boring at Lucknow, in the Indo-Gangetic plain, passed through 1,336 
feet of alluvial deposits consisting chiefly of more or less sandy clays. 
A still more remarkable case (see page 118) is found in the Great 
Valley of California, where, according to Ransome, borings in the 
San Joaquin valley at Stockton have penetrated 2,000 and 3,000. feet 
respectively in unconsolidated fluviatile deposits consisting chiefly of 
fine sands and clays. Professor Davis, speaking of the aggraded plains 
of Turkestan, says, “ Certainly no one who sees the river-made area 
of the plains of Turkestan can doubt the capacity of rivers to lay down 
extensive fine-textured deposits” (Davis, p. 55). 
Crush. The general lack of similarity of the rocks of the three 
basins to crush conglomerates, as shown by the comparisons on page 
250, render any further consideration of this mode of origin unneces- 
sary. 
Glacial. Professor Shaler has been the most earnest supporter of 
the glacial hypothesis (Shaler et al., p. 64-67), though Dodge (page 
103) also recognized the possibility of such origin. From the com- 
parisons on pages 250 and 251 it appears that no deposits definitely 
comparable to boulder-clay have been observed among the deposits 
of the several basins and that no definitely faceted pebbles or pebbles 
bearing striae have been found. Furthermore, the conglomerates 
and accompanying sediments do not lie upon glaciated surfaces, but 
Instead they rest upon a surface long subjected to subaërial decay. 
These facts show that glaciers could not have been the direct agents 
by which the Carboniferous sediments of this region were deposited. 
Indirect glacial action, however, is not precluded. Indeed, there 
are a number of reasons for believing that glaciers were active agents 
ın Preparing the material for deposition. ‘The tumultuous arrange- 
ment of pebbles, not faceted nor striated, but more or less water worn, 
observed at some localities, might be explicable as merely a result 
of fluviatile action, but it is eminently characteristic of fluvio-glacial 
