616 



STRATIGRAPHICAL GEOLOGY 



rasping, graving, and moulding tool. In most cases it is found 

 that the grooves run parallel to the main valleys of a district, and 

 in many cases when the directions are marked on a map it is seen 

 that they radiate outward in all directions from some central 

 mountain tract ; but occasionally they run in one direction across 

 some tract of country without any reference to its valley system, 



12 II 10 9 8 



543 



58 



Fig. 202. MAP SHOWING THE OLACIATION OF SCOTLAND AND THE NORTH 



OF IRELAND (J. K. Kilroe). 

 (Reproduced by permission of the author and the Council of the Geological Society.) 



as if the ice had been locally deflected from its natural course. 

 This system of grooves and striations is often called the glaciation 

 of a district or country. 



Thus the plotting of the principal lines of striation in Scotland 

 has shown that country to have been an independent centre of ice- 

 dispersal, and that at the time of maximum glaciation it was wholly 



