﻿68 DR. WOOLACOTT ON THE SUPERFICIAL DEPOSITS, ETC. ' [Feb. I905, 



vary in volume with change of season and climate. So far as the 

 available evidence from the district under consideration goes, there 

 does not seem to be anything pointing to an Interglacial Period or 

 Periods. The deposits of sand and sandy clay found intercalated in 

 the true Boulder-Clay are, as a rule, most irregular in position, and 



Fig. 2.— Pre- Glacial (or Glacial) gravel-deposit at Newbiggin, 

 near the month of the WaiisbecJc. 



[From a photograph taken by Dr. J. A. Sraythe in 1903. The gravel-deposit 

 here rests upon Coal-Measures, and is overlain by Boulder-Clay.] 



vary laterally in thickness. Some of the thicker deposits may 

 represent epochs when the ice was melting more quickly than others, 

 but whether they can be considered as in any sense ' Interglacial ' is 

 very doubtful. 



While several eskers occur upon the Boulder- Clay in the north of 

 Northumberland, outside the area of the coalfield, very few forma- 

 tions of this character have been noticed within the district under 

 review. There is, however, near Grindon, about 2 miles west of 

 Sunderland, at an elevation of 300 feet, a hillock of sand and gravel 

 some 60 feet high, which partakes of this nature. 



The mounds of sand and gravel, often designated 'Drift,' that are 

 found resting upon the Boulder-Clay, principally in the east and south- 

 east of County Durham, may have been produced when the enormous 



