136 COURTS WITH OR WITHOUT LAKE-BASINS. 



Subsequently to the corrys having been in part 

 formed by marine action, they seem to have been 

 enlarged and deepened by ice, as ice apparently 

 would have more power than the sea to form the 

 rock-basins so often associated with them ; for, as 

 shown previously, it would be more capable of lift- 

 ing and carrying away all the blocks loosened in 

 the breaks, besides raising additional blocks ; for as 

 the water from the ice froze in the crevices and 

 cracks, it would loosen and quarry out other blocks, 

 and raise them up into the influence of the ice- 

 stream. 



Although we are inclined to believe that ice was 

 the principal agent in excavating out the rock-basins 

 of the corrys, yet we should point out that water also 

 is capable of excavating somewhat similar hollows, 

 and in an arctic sea may have had powers that are 

 unknown to us of the temperate zone. The forma- 

 tion of those peculiar cylindrical hollows, often called 

 " churn-holes," found in some rocks on the sea- 

 coast, and in river-beds, seems to point to a process 

 by which the sea might grind out deeps in the floors 

 of the corrys. " Churn-holes " are not uncommon, 

 and we find they always occur in rocks containing 

 nodules, concretions, or some other kind of macula 



formed cliffs, yet it is probable that they in part existed prior to the 

 current, especially at high altitudes, and were preserved from modifica- 

 tion or obliteration by an envelope of snow and ice, while lower down 

 marine action was changing the form of the old ground. 



