166 MAN AND THE GLACIAL PERIOD, 



was, so far as its lower strata were concerned, unable to 

 ascend so steep an acclivity, and was cleft, and flowed to 

 right and left. The upper ice, being of ice-sheet origin, 

 would be relatively clean, and this flowing straight over 

 the top of the obstruction would glaciate the country 

 with such material as was lying loose upon the ground or 

 could be dislodged by mere pressure. It would appear 

 from published descriptions that the Isle of Arran offers 

 the same problem, and I would suggest the application of 

 the same solution to it. 



" Marine shells occur in the Manx drift, but only in 

 such situations as were reached by the ice laden with 

 foreign stones. They present similar features of associ- 

 ation of shells of different habitat, and perhaps of geo- 

 logical age, to those already referred to as being com- 

 mon characteristics of the shell-faunas of the drift of the 

 mainland. Four extinct species of mollusca have been 

 recognised by me in the Manx drift. 



" The Manx drift is of great interest as showing, per- 

 haps better than any locality yet studied, those features 

 of the distribution of boulders of native rocks which at- 

 test so clearly the exclusive action of land-ice. There 

 are in the island many highly characteristic igneous 

 rocks, and I have found that boulders of these rocks 

 never occur to the northward of the parent mass, and 

 very rarely in any direction except to the southwest. 



" dimming observed in regard to one rock, the Foxdale 

 granite, that whereas the highest point at which it occurs 

 in situ was 657 feet above sea-level, boulders of it occurred 

 in profusion within 200 feet of the summit of South Bar- 

 rule (1,585 feet), a hill two miles only, in a southwesterly 

 direction, from the granite outcrop. 



" They also occur on the summit of Cronk-na-Irrey- 

 Lhaa, 1,449 feet above sea-level. The vertical uplift has 

 been 728 and 792 feet respectively. 



" In the low grounds of the north of the island a finely 



