418 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 23, 



the depressions ; and the sharply defined brinks of the gullies they 

 have excavated can at once be distinguished from the neighbouring 

 form of ground. But streams in many places have made channels 

 where little or no previous depression existed. The steepness of 

 their sides varies with the compactness of the drift, the absence of 

 springs, &c. But though the streams have been flowing in their chan- 

 nels ever since the Glacial period, rain has not been able to bevel down 

 the sides of these channels to a lower average angle than 30°. Geo- 

 logists ought therefore to hesitate before attributing to rain the ex- 

 cavation, in hard rocks, of valleys the sides of which rise above the 

 river- channels at an angle of only 4° or 5°. 



c. Origin of Drift Escarpments and Valley -plains. — As already re- 

 marked, depressions must have been formed in drift deposits before 

 their elevation above the sea*. As waves at a stationary level are 

 now wearing the slopes of these depressions back into cliffs, it is rea- 

 sonable to suppose that the cliff-hnes now bounding valley-plains 

 which have partly or wholly risen above high- tide level have been 

 formed by wave-action. Rivers have wandered over these plains, 

 and during floods deposited sand or loam. In many places thej have 

 attacked the cliff-lines and worn them back into horseshoe-shaped 

 curves. But some of the concavities in the drift escarpments bound- 

 ing low-level valley-plains have escaped river- action, as would appear 

 from the direction of the dip of the ground under them, from their 

 form relatively to the old gullies which abruptly break their conti- 

 nuity, from transverse sections of the bases of the escarpments re- 

 vealing the kind of agency to which they were last subjected, &c. 



The river Eibble, at E,edscar Cliff, near Preston, has evidently only 

 lately attacked the concave escarpment, a part of which it is under- 

 mining and carrying away, while a great part of the cliff- line on 

 both sides of the valley-plain traversed by this river shows indica- 

 tions of its having been formed by the sea f. 



5. Smoothed E-ock-stjefaces and Dkiets oe the Fueness Penijs'sula. 



Between Carnforth and Ulverstone, along the sea-coast, several 

 sections of drift may be seen exposed. To the west of Grange the 

 hard Lower Boulder-clay appears in full force, and looks either like 

 an old beach under an escarpment, or a fringe of a formerly extensive 

 deposit. At Cark Station gravel and sand make their appearance. 

 In the neighbourhood of Ulverstone one cannot proceed very far in 

 observing drift-sections without seeing the importance of beginning 

 his researches with examining the forms presented by the rock- 

 surfaces of the district. 



a. Distinction between Glaciated, Rain-worn, and Sea-worn Rock- 

 surfaces. — Ice, especially land-ice, is a planing agent. It uniformly 



* In each successire drift deposit depressions must have been scooped out 

 while the deposit was under the sea, as these depressions are filled up with over- 

 lying drift. The latest depressions formed in drift must have risen above the 

 sea without being filled up excepting by postglacial warp, &c. 



t Mr. De Ranee, of the Geological Survey, accompanied me when I examined 

 the drift escarpments near Preston, and agreed with the conclusions at which I 

 arrived. 



