of Edinburgh, Session 1878-79. 
269 
But even if it were possible to suppose that a glacier had been 
formed at the head of the valley, and that it overspread East 
Lothian, I find it difficult to understand how rocks, so nearly 
vertical as those at North Berwick and on the railway could have 
been striated in the way suggested by Mr Stevenson. Stones or 
pebbles at the bottom of a glacier might, by the weight of the 
glacier upon them, be made to striate rocks below the glacier, 
these rocks forming the floor upon which the glacier moved. But 
rocks which were vertical , or nearly so, could not be so operated 
on ; and there are no observations to warrant the supposition that 
pebbles are ever imbedded in the ice and protruding from the 
side of a glacier so as to groove the vertical sides of a hill. 
The infinite number of the striae on these steep rocks at Linton 
and North Berwick Law is also a circumstance most unfavourable to 
the supposition that they were formed by stones protruding from the 
side of a glacier. On the other hand, a thick mass of boulder-clay, 
full of hard pebbles, would be quite capable of striating, if the clay 
containing them were pushed forward and pressed on a rock surface. 
There is another feature which bears on the nature of the striating 
agent. Mr Stevenson correctly pointed out that whilst most of the 
ruts and striae on North Berwick Law were horizontal, some striae 
rose upwards towards the east at angles from 4° to 20°. On the 
railway rock near Linton I observed the same feature. If the striae 
were formed by stones protruding from the side of a glacier, they 
would all be parallel. Their want of parallelism can be more easily 
explained if a mass of detritus was the agent. 
There is one circumstance which appears almost conclusive against 
a glacier having been the agent of striation, at 'all events in the 
valley of the Forth, and strongly favourable to the theory I have 
indicated in this paper. 
This circumstance is the facility with which the striating agent 
is shown to have been deflected from its normal course by trivial 
obstructions. Thus at Linton, in consequence of the rock, on which 
the striating agent impinged dipping due north, at a considerable 
angle, that agent, when it came in contact with the rock, was 
deflected from its E.S.E. normal course to a direction of due south, 
being a deflection of 22°. In the railway cutting, where the slope 
of the rock was greater, and therefore more obstructive, the striating 
