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THE JOURNAL OF GEOLOGY. 



faces. The lines of each series are parallel with one another, but 

 the lines of separate series may cross each other at any angle. 

 Multiple series on a single face are not rare, though less com- 

 mon than single series. Multiple series on multiple faces are 

 rather infrequent, yet every student of the drift has seen them 

 many times. Similar markings are not unknown on the well- 

 rounded stones of the drift, though they are here much less 

 abundant than are those of sub-angular forms. 



Fig. I. Characteristic forms of small stones taken from unstratified drift. The 

 contrast in form between these and water-worn pebbles is evident at a glance. 



These markings, or strice, as they are called, do not affect all the 

 stones, or even all the sub-angular stones of the drift. If fifty per 

 cent, of those occurring in the unstratified drift of any locality 

 are striated, this is to be looked upon as a large proportion. On 

 the other hand, even the unstratified drift locally contains so few 

 striated stones that a single one is hard to find, even when 

 good exposures are at hand. So far as concerns abundance of 

 striae, something depends on the relative proportions of coarse 

 and fine materials. Much also depends on the differences in 

 hardness between the various constituents. The striae are much 

 more abundant on the softer stones, such as limestone, than on 

 the harder, such as quartzite. In much of the stratified drift, 

 striated stones are rarely found. But in certain phases of it, 

 they are no rarity. Where they are abundant, their forms are 

 likely to be sub-angular, just as in the unstratified drift. Striation 

 of surface, and sub-angularity of form, seem to go together. 



