INDICATIONS OF GLACIAL ACTION IN CORNWALL. 185 



present beaches below them, and. shows an arrangement of their 

 materials mainly agreeing with the "drift beds" of Northern 

 Britain. 



Fig. 1 represents a typical section of these beds at Porth- 

 gwidden Cove, St. Ives ; its lower part is composed of water- 

 worn pebbles of granite and hornblende, with a few chalk 

 flints, and of coarse gravel mixed with brown siliceous sand. On 

 the top of this stratum is a bed of fine sand ; and resting on the 

 whole are large angular blocks of hornblende rock embedded in 

 loam, both of which have obviously been derived from the ad- 

 joining higher ground. These rocks have all their angles on and. 

 show no indication of removal by water, and many of them are 

 ■of considerable size and weight, so that it is difficult to conceive 

 how they could have been removed to their present position 

 without the carrying action of a great sheet of land-ice descending 

 by gravitation from the land above. 



Again in the bed of " drift " (Fig. 2) exposed in the cliff under 

 Godrevy Farm and resting on a similar bed of siliceous sand, I 

 found a large mass of slate which appeared to have been gouged 

 out from the hill above and pressed into the sand-bed by ice 

 action, and then covered by angular debris from the high land 

 adjoining. An illustration on a much larger scale is afforded by 

 the country between St. Ives and St. Just. The high granite 

 hills of the interior slope rapidly towards the sea on the north, 

 having a broad terrace at their foot mainly composed of granite, 

 with patches of killas near the coast, as shown by Plate No. II. 

 The decomposed granite has formed on the surface a bed of loam, 

 which is scanty on the steep hill-side, but gradually thickens to 

 «ix and ten feet on the more level surface of the terrace below. 

 The loam contains some waterworn pebbles of rock brought from 

 a distance, indicative of an alluvial formation. At the foot of the 

 steep portion of the hill the boulders of granite are most abundant 

 and are piled up in great confusion ; but further down the slope 

 they rest chiefly upon the surface of the loam and are very seldom 

 embedded in it. jThe boulders are scattered over the surface of 

 ,the granite and of the killas beyond. 



It is obvious, from the section, that during the formation of 

 the loam there was an alluvial action in operation, but not 

 jpowerful enough to remove heavy blocks of stone, and that 



