1854.] CUMMING — GLACIAL DEPOSITS, ISLE OF MAN. 



213 



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presented (if we except the northern area 

 consisting wholly of pleistocene deposits to 

 the extent of 50 square miles) the general 

 outline which it now does. At what period 

 the great denudation took place which planed 

 down to the same level both sides of ex- 

 tensive faults which took place in the older 

 strata subsequent to the deposit of the car- 

 boniferous series, we have no distinct evi- 

 dence. The boulder- clay consists, in greatest 

 part, of materials derived from the older 

 rocks in the immediate neighbourhood, as I 

 have before pointed out ; and it lies right 

 across the faults which have been so denuded 

 and planed down evenly on both sides*. 



Over the whole of the southern area of the 

 Isle of Man, wherever the limestone is un- 

 covered, glacial groovings and scratches are 

 distinct ; their general direction being very 

 nearly magnetic east and west, i. e. from N. 

 59° E. to S. 59° W. by meridian, and quite 

 independent of the dip of the limestone-beds. 

 The scratchings extend down to the present 

 high-water-line ; and even below it, wherever 

 they have been jjrotected by the stiff clay 

 from the present action of the sea. 



I would direct particular attention to the 

 patch of limestone existing between Port St. 

 Mary and Perwick Bay, of about 60 acres in 

 extent. The general dip of the beds is from 

 the fault which runs nearly magnetic east and 

 west ; and the regular groovings are in the 

 direction of this fault ; but there are frequent 

 minor cross scratchings which vary several 

 degrees from this general direction. This ap- 

 pears to me to be attributable to the action 

 of shore-ice. 



There are also appearances as if the 

 boulder-clay had been forced violently 

 amongst the different beds of the limestone ; 

 and fragments of the latter are torn up and 

 carried forward ; and these remain angular 

 though much scratched, at no great distance 

 in the mass of clay which now covers up the 

 limestone-beds. (See section.) 



A section of 400 feet in length, which 

 I have made in a direction east and west by 



* See sections and maps of the papers above re- 

 ferred to. 



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