34«0 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the anchorage of tough clay in Castletown and Port-le-Murray Bays, 

 for which reason it is inserted conjecturally in the sections made 

 across the basin over those areas (see Plate XVII. fig. 3). 



There are certain appearances in the boulder clay formation in the 

 neighbourhood of Ronaldsway, which may lead to the conclusion that 

 the disturbance which has produced the cracks and faults running 

 N. 80° E. mag., and nearly at right angles to that direction, did not 

 take place till after some deposit of the boulder clay. Whenever 

 that disturbance did take place, it appears to have been accompanied 

 with a discharge of heated gaseous vapours with acids, since the lime- 

 stone along the cracks and upheaved portions has become burnt, cry- 

 stalline and metamorphic. But what is most remarkable is, that 

 the boulder formation is also in some way affected in the same 

 spots, parts of it having become a hard and burnt-looking mass, 

 which has resisted the action of the sea, whilst the rest has been de- 

 nuded from the unaltered limestone in the immediate neighbourhood. 

 It may be possible to explain this phsenomenon by supposing that a 

 cementing matter has in some way been obtained from the subjacent 

 altered limestone, by long-continued contact and the action of water. 

 If however the former hypothesis be adopted, it will also enable us 

 to account for the elevated position of the boulder deposit on the 

 Brough above Coshnahawin, and may assist in determining that the 

 second of the disturbances which effected the elevation of that hill, 

 was that which passed in a direction nearly compass east and we'st, 

 producing also faults which run nearly compass north and south*. 



Upon a general review of the boulder clay, or pleistocene forma- 

 tion of this island, it seems not unreasonable to conclude that there 

 was a more arctic climate at the period of its deposit than now ex- 

 ists in this latitude. If we examine carefully the striations upon 

 the subjacent rocks, we shall perceive that many of them are not 

 continuous, but have the appearance of being struck out by a sharp 

 blow of some hard object brought suddenly in contact and then 

 passing over the surface. I have examined very closely the action 

 of the waves of the present sea driving boulders over the surface of 

 the limestone where it is exposed in many places to the action of the 

 breakers, and can perceive no similar effect now produced; and I am 

 rather inclined to believe in the action of ice drifting from the E.N.E., 

 conveying fragments of the rocks from the north-west of England and 

 south of Scotland, scratching, grinding down and polishing all the 

 more prominent surfaces in the different channels through which it 

 might be compelled to pass. We can readily conceive that in such a 

 sea the action of the breakers driving forward frozen masses of gra- 

 vel and boulders would have a powerful effect in the degradation of 

 the shores ; and also that large accumulations of detritus from the 

 clay schists of the higher portions of the island (reaching to a height 

 of between 1500 and 2000 feet) would be brought down by the 



* I had long sought for some fragment of the Barrule granite in the boulder 

 clay, and very lately I have succeeded in obtaining two rounded boulders of this rock, 

 which however have set at rest the question as to whether that granitic boss had 

 been upheaved before the boulder clay was deposited. 



