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 



