﻿1851.] BRICKENDEN ON THE BOULDER CLAY NEAR ELGIN, 291 



Fig. 3. — Section taken at a right angle to the face of the Escarp- 

 ment ; Linksjield Quarry. 



a. Oolitic series. c. Intercalated Boulder-clay, with oblique 



b. Devonian Limestone. seams of purple clay. 



b'. Polished surface of the Limestone. d. Superficial Drift and Alluvium. 



Having thus stated a few particulars regarding the intercalated 

 drift at Linksfield, and presuming that, by the various appearances 

 which it exhibits, the fact of its intrusion into the position it now 

 occupies is established, it becomes a very interesting matter to in- 

 quire in what manner and by what external force such intrusion has 

 been effected. We can imagine that a mass of yielding clay, arrested 

 at the base of an escarpment or outcrop of strata, might have been 

 injected between them, in much the same manner as igneous or molten 

 masses between some of the stratified formations, provided that cer- 

 tain conditions were fulfilled, of which the chief would be that the 

 propelling power should exceed that of the resistance opposed to it, 

 and that the movement of the injected mass should be confined wholly 

 to the interstratified position referred to. I therefore presume that 

 the Boulder-clay, having originally accumulated at the base of the 

 oolitic outcrop at Linksfield, and having gained an entrance into the 

 position held by its softer and subjacent beds, had been subjected to 

 the action of vast and extensive masses of ice, which, by continuing 

 to press onwards the accumulations of clay retained beneath it, had, 



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