332 TYNEDALE ESCAEPMENTS ; 



may well have dissected out its structure of hard and soft parts 

 upon watersheds. 



In summing up the evidences for time, in the case of the Weal- 

 den Escarpments, Professor Ramsay concludes, from quite other 

 data, that they have at least been exposed since the Pliocene ; 

 and he personally is inclined to think, from the physical evi- 

 dence, that they were exposed during the Pliocene. Even the 

 former estimate, he remarks, implies ^'a lapse of time so long, 

 that by natural processes alone nearly half the marine mollusca 

 and probably nearly all the terrestrial species of mammalia of 

 the world have disappeared, and have been slowly replaced by 

 others." Professor Eamsay continues, ''This may mean little 

 to those who still believe in the sudden extinction of whole 

 races of life, but to me it signifies a period analogous to the dis- 

 tance of a half-resolved nebula, the elements as yet being 

 wanting, by means of which we may attempt to calculate its 

 remoteness."* 



Effects of the Glacial Period upon Tynedale Escarpments. — 

 Passing away from the larger section of the subject, a question 

 of much interest awaits us. To what extent were these escarp- 

 ments modified by the passage of the glaciers over them ? 



It is now one of the most familiar facts of geological science 

 that all Korth Britain, and many northern lands besides, were 

 invested with what was literally a flowing robe of ice.f In this 

 part of I^orthumberland large valley - glaciers pressed down 

 through Pedesdale and IJ^orth Tyne upon the main valley ; also, 

 however curious the fact, a spreading ice-sheet moved over the 

 w.atershed from the west, bearing with it reddened clay from the 

 vale of Eden, and granite boulders from beyond the Sol way, 

 and slid towards the l!^orth Sea. Tynedale crags, both near the 

 valley and on the watershed, were deeply buried : some had the 

 ice moving along them, others had to breast it ; and all suffered 

 more or less erosion. 



* Phys. Geol. and Geog. of Great Britain, 5th Edition, p. 345. 



t The general fact that Northumberland Avas no exception has been long known. 

 See Howsc, Trans. North of England Institute Mining Engineers, Vol. XIII., p. 169. 



J 



