-'.<, OUTLINES OF FIELD-GEOLOGY PART I 



The ice must evidently have moved from the quarter to 

 which the smoothed faces are presented, and towards 

 the quarter to which the rough parts are turned. This is 

 shown in Fig. 83, where the arrow indicates the trend of 

 the ice movement. The way in which an observation of 

 this kind may be indicated on the map is shown in the 

 index of signs in Fig. 4. By a sufficient number of such 

 observations in a district, the path of the ice across it 

 may be clearly expressed. 



Another useful method of supplementing this evi- 

 dence from rock - striations as to movements of the 



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Fu.. 84. Striated stone from the boulder-clay. 



ice cannot usually be put into practice until after the 

 observer has made some considerable acquaintance with 

 the geology of a wide region. In countries which 

 have been under ice, and where the rocks retain the 

 characteristic ice-markings, the surface commonly presents 

 abundant accumulations of boulder-clay, gravel, and other 

 deposits belonging to different conditions of the long 

 Glacial Period. A search through the stones and boulders 

 of these deposits will in most cases disclose the fact that 

 the fragmentary materials have been moved a greater 

 or less distance from their parent rocks. In the clays, 



