ANCIENT GLACIERS IN EASTERN HEMISPHERE. 159 



Wolds appear to have been completely whelmed beneath 

 the ice. 



" The most remarkable of the deposits in this area is 

 the Great Chalky Boulder- Clay, which consists of clay con- 

 taining much ground-up chalk, and literally packed with 

 well-striated boulders of chalk of all sizes, from minute 

 pebbles up to blocks a foot or more in diameter. Associ- 

 ated with them are boulders of various foreign rocks, and 

 many flints in a remarkably fresh condition, and still re- 

 taining the characteristic white coat, except where par- 

 tially removed by glacial attrition. 



" One of the perplexing features of the glacial phenom- 

 ena in the eastern counties of England is the extension 

 of true chalky boulder-clay to the north London heights 

 at Finchley and elsewhere ; for only the faintest traces are 

 to be found in the gravel deposits of the Thames Valley 

 of any wash from such a deposit, or from a glacier carry- 

 ing such materials. 



" It has been suggested that the deposit may have been 

 laid down in an extra-morainic lake, or in an extension of 

 the North. Sea, but these suggestions leave the difficulty 

 just where it was. If a lake or sea could exist without 

 shores, a glacier-stream might equally dispense with banks. 

 Within the area of glaciation, defined above, abundant 

 evidence of the action of land-ice is obtainable, though 

 striated surfaces are extremely rare — a fact attributable to 

 the softness of the chalk and clays which occupy almost 

 the whole area. Well-striated surfaces are found on the 

 harder rocks, as, for example, on the oolitic limestone at 

 Dunston, near Lincoln. 



"Mr. Skertchly has remarked that the proofs of the 

 action of land-ice are irrefragable. The Great Chalky 

 Boulder-Clay covers an area of 3,000 square miles, and at- 

 tains an altitude of 500 feet above the sea-level, thus be- 

 speaking, if the product of icebergs, ' an extensive gath- 

 ering-ground of chalk, having an elevation of more than 

 12 



