756 ON THE GEOLOGY OF THE ISLAND OF AQUIDNECK, 
show, in the character of the deposits or in the physical condition 
‘of the boulders they contain, indubitable evidence of some action 
other than those usually’ operative on the surface of the earth. 
Wherever, as in the nagelfluh of Switzerland or other similar accu- 
mulations, we have wide extending shells of boulders and gravel, 
we are clearly justified in suspecting ice action, when, as in all 
cases of conglomerates of wide geographical extension which I 
have examined, the pebbles are not formed with the regular out- 
lines which necessarily occur where the shaping of the masses is 
the result of moving water. We are bound to believe that peb- 
bles of all sizes, which have been worn to their shape by running 
water, must tend to assume regular forms, the major axis of which 
will be coincident either with the greater lengths of the pebbles 
or with their lines of greatest hardness. 
In any case the pebbles will generally assume more or less 
oblately spheroidal forms. On the other hand, materials which have 
received their shapes under glacial action will generally be free from 
those results which come from the uniform friction of one pebble 
against another, inasmuch as such movements will be impossible 
while the fragments are in the grip of the ice. The nature of the 
conditions is such that the pebbles will be worn by being held in a 
fixed position with one side turned to the abrading agent, the 
others being for the time protected from wear. With the constant 
changes occurring in the moving ice one pebble will frequently 
come to have several facets cut upon it in this way, and many . 
pebbles in succession will be subjected to the same sort of wear. 
In accumulations of unaltered glacial deposits we always find 
pebbles having this many faceted character which results from 
the successive wearing. The only difficulty is that many, often by 
far the larger part of the mass, are made up of pebbles which have 
gotten their shape without actual attrition, being simply rounded 
by chemical action, or keep their original form ; but, in any case 
where many pebbles with a faceted character occur in a conglom- 
erate it may be safely concluded that it has been formed by ice 
action. : 
Pebbles having the above described characters occur in abun- 
dance throughout the unaltered part of the conglomerate which 
underlies the Rhode Island coal. This with the other features 
may be taken making it pretty nearly certain that it had a glaci 
origin. It must be noticed, however, that in no case have the 
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