S36 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



of age of this deposit, since the beds pass upwards into the diluvial 

 drift or till, especially in the northern part of the island. This dif- 

 ficulty arises partly from the want of any regular stratification and 

 the presence throughout of transported blocks, and partly from the 

 partial denudation and removal of the boulder clay and its re-arrange- 

 ment amongst the drift ; whilst it seems probable that causes re- 

 sembling those which produced the true diluvium, though not per- 

 haps of equal intensity in the same direction, may have operated 

 during the whole period of the boulder clay formation*. 



In the northern district of the island, the rake of the tide in the 

 channel, assisted no doubt by the ordinary atmospheric action and 

 by violent wind and rains, is constantly removing large masses of 

 the cliff on the eastern and western coast, and exposing the whole 

 series to view. It may be usefully studied a few hundred yards 

 south of the town of Ramsey, where it abuts against the schist, 

 which is seen dipping rapidly to the north (see section, Plate XVII. 

 fig. 4). The more loamy lower portion is not there discovered in 

 the cliff, which is hardly more than thirty feet high, but it appears 

 to form the good holding ground in the south of Ramsey Bay ; and 

 a stick thrust down into the sand between high and low water 

 reaches a hard clay, which no doubt belongs to this part of the for- 

 mation. As we proceed northwards from Ramsey, we obtain in the 

 cliffs between the Dog Mills and Point Cranstal a finer development 

 of the series and access to the more loamy portion. 



The boulders are described by Mr. Strickland f as consisting of 

 slate-rock, quartz, old red sandstone, carboniferous limestone, gra- 

 nites, porphyries and chalk flints ; and he mentions that all the rocks 

 except the two latter occur in situ on the island. The granites how- 

 ever of the northern deposit of the boulder clay, as far as I have yet 

 seen, are not the insular granite, nor have I discovered any chalk 

 flints in that part of the series which I consider really belonging to the 

 pleistocene series. In consequence of the diluvium overlying the 

 boulder clay formation, it frequently happens that when the cliff is 

 undermined, the boulders of the two separate series become mixed 

 together on the sea-shore, and even on the slope of the cliff; and much 

 caution is requisite before deciding to which formation an individual 

 boulder may belong |. The boulders of red syenite and porphyry 

 agree very well with hand specimens from Cumberland, and one of 

 them with the Skiddaw granite. As porphyritic greenstone occurs 

 largely both in the south and centre of the island, the blocks of 

 it in the boulder clay seem of uncertain origin ; but most probably 

 those in the northern boulder formation are foreign, and those in 



* At Cranstal Head, in the north of the island, there is an appearance of alter- 

 nations of larger masses of gravel and transported matter associated with the finer 

 clays and sands. 



t Proc. Geol. Soc. vol. iv. p. 8. 



X Since writing the above I have found a chalk flint in the boulder clay of 

 Hango Hill, at the head of Castletown Bay, in a position which seems to render 

 it almost certain that it belongs to the formation we are now considering. See 

 woodcut, p. 338. 



