ON CERTAIN STTRFACK I'EATURKS, ETC. 191 



perpetual decree that it cannot pass it ; and though the waves 

 thereof toss themselves, yet can they not prevail : though they 

 roar, yet can they not pass over it." The extensive sand-dunes 

 on many parts of the coast of Northumberland form an almost 

 impassable barrier to the encroachments of the sea, but boulder- 

 clay banks are being gradually removed. 



From the almost demonstrable deductions of geologists and 

 astronomers it appears that the beds of clay between North 

 Shields and Tynemouth must have been deposited when a mass 

 of ice, probably two thousand feet in thickness, was pressing its 

 way from the interior to the sea and grinding the earth and 

 rocks in its course into the clay we now find on our coast. 



Existing forces have attacked and dispersed in half a century 

 huge masses of the clay that may have taken the Glacier Ice 

 thousands of years to grind down and deposit in the state in 

 which we find it in our cliffs. There seems to be no haste in 

 the operations of nature in building up : the haste is in the pro- 

 cess of disintegration and dispersion. 



XII. — On certain Surface-Features of the Glacial Deposits of the 

 Tyne Valley. By G. A. Leboitr, M.A., F.G.S., Professor of 

 Geology in the Durham College of Science, Newcastle-on- 

 Tyne. 



Teavellees by the Newcastle and Carlisle Eailway are familiar 

 with the fine exposures of sand and gravel between Eiding Mill 

 and Corbridge, and with the short tunnel which pierces these 

 deposits opposite Thornbrough Wood. 



These sands and gravels are Glacial in origin and newer than 

 the Boulder Clay on which, indeed, they lie. More than one 

 opinion is held respecting their mode of formation and as to their 

 exact age within the Glacial Period. Into these matters I do 

 not propose to enter at present. It will be suflicient for my 

 purpose to state that the series in question is of considerable 



