132 



NOTES ON THE DRIFT DEPOSITS 



of the hard rocks in the beds of gravel are of the same kinds 

 as those found in the till, however much their external cha- 

 racters may have been altered. In all probability, therefore, 

 the former is merely the debris of the latter. 



On the upraising of the till from the bottom of the sea, its 

 surface would soon become liable to the abrading action of 

 the waves, and thus furnish rocks for the sands brought by 

 currents from the neighbouring new red sandstone coast, just 

 as the present clifis furnish the pebbles for the shingle beaches 

 at Blackpool. 



The rocks in the till have, no doubt, come from a consider- 

 able distance, especially the lias and chalk specimens, which 

 are not now found in situ nearer than the north-east coast 

 of Ireland. 



The rocks in the till at Manchester, taken on three diflfer- 

 ent sides of that town, gave mean results as follows :* — 



Partly 



Total. Angular. Rounded. Rounded. 

 Granites, greenstones, and other 



igneous rocks 21 5 10 6 



Slates and Silurians 21 3.66 9 8.33 



Mountain limestones 6 13 2 



Coal measures 49.33 25.33 19 5 



New red sandstones 2.66 2 • 0.66 



Striated rocks 1.66 



In the brick-yard near the railway station at Blackpool, 

 the rocks were as follows : — 



Partly 

 Total. Angular, Rounded. Rounded. 

 Granites, greenstones, and other 



igneous rocks 49 17 20 12 



Slates and Silurians 32 5 16 11 



Mountain limestones ..<■ 6 3 2 1 



Coal measures 9 4 3 1 



New red sandstone and superior 



rocks 4 12 1 



Striated rocks 6 slates and Silurians. 



♦ Memoirs of the Lit. and Phil. Society of Manchester, vol. viii. (new series) 

 p. 224. 



