SAYLES: THE SQUANTUM TILLITE. 143 
of the earth, the till contains no striated pebbles. It is not always 
possible to say why striae are wanting in some regions. Where the 
pebbles are mostly of some very hard rock like quartzite, the striae, 
on account of the hardness of the substance, may be nearly absent. 
I mention this absence of striae because so many geologists, on this 
account, doubt the glacial origin of certain tillites. 
Striated stones are frequently blunted at one or both ends, or turned 
to a point at one end and blunted at the other end. They are also 
in many cases bevelled on one or more sides. If a stone is too hard to 
take the striations the blunting or bevelling effects may still be present. 
In addition to the angular, subangular, oblong, facetted, bevelled, 
striated pebbles, there is another mark of glaciation on stones in the 
drift which has not received sufficient attention from geologists. This 
characteristic, so often mentioned to me by Prof. J. B. Woodworth, 
is of as much importance in determining the glacial origin of till or 
tillite as the striated stones. I have reference to the concave fractures 
which appear on many glaciated stones. These are as positive a 
mark of glaciation as striae, and fractures of this nature can be found 
as frequently as striae or even more so. Such fractures must be pro- 
duced by crushing under a tremendous pressure of ice, in which case 
the fractured pebble would probably lie between another rock frag- 
ment and a rock-floor, or where there is no rock-floor, between two 
other rock fragments (Woodworth, 1912, p. 76-77). 
As a rock-floor or striated pavement has been found beneath several 
tillites, some geologists have not been convinced of the glacial origin 
of tillites which have no grooved rock-floor or striated pavements. 
The principal objection to Professor Coleman’s glacial deposit in the 
Huronian was just this point; but no rock-floor in the case of some 
accepted tillites has been found (Coleman, 1908, p. 354). 
Glacial deposits are made up of a great variety of rocks. In till or 
tillite may be found rock fragments which have been transported many 
miles from the parent ledge. This great variety is not found in gravels 
formed under cliffs where there has been no glacial action, nor in local 
river-gravels where the stream has had a short course and acted on 
the local rocks. 
The crushed fragments of the till or tillite show fresh rock and not 
weathered materials. 
In many deposits of till and tillite pieces of the local, underlying, 
at the time unconsolidated beds over which the glacier has passed 
may be found, together with those derived from a distance. 
According to Stone (1899, p. 29-30), the lower part of a bed of till 
