22 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [MaV 17, 



deposited simultaneously, or in a violent manner, as this is a common 

 character in all mud formations. 



In the sections now exhibited, the brown clay rests on a pretty 

 even surface of the till. In some other places however there was 

 proof that the till had been exposed to erosive action before the de- 

 position of the immediately superior formation. In many places it 

 was worn into hollows, as if part of it had been removed by the action 

 of water : one of these hollows was very remarkable, being about five 

 or six feet wide by three or four deep, and closely resembled the 

 channel of a small stream. It was also filled with gravel and sand, 

 in all respects like that found in such a stream at present. It was 

 seen with the same characters on both sides of the cutting, but how 

 far it continued beyond could not be known. I had no doubt that 

 it had been formed by some stream of rummig water, which, if we 

 suppose the till deposited in the sea, would imply that it had been 

 elevated and again depressed for the deposit of the superior beds. 

 This elevation of the till to the surface, permitting the action of the 

 atmosphere on any shells or other remains contained in it, may 

 perhaps accomit for the rarity or rather entire absence of fossils in 

 this deposit. 



The second subject which I should wish to notice has reference 

 to the transport of erratic blocks. As already stated, this has begun 

 even in the earliest period, during the deposition of the till, and has 

 continued down to the most recent. They occur in the brovra clay 

 represented in the sections resting on the till, and in a higher deposit 

 of gravel and boulders which often covers the deposit of fine strati- 

 fied sand seen filling a hollow in the brownii clay in section fig. 3. 



Fig. 3. 



Stratified sand. 



They are frequently found lying completely exposed on the surface, 

 and in this case may never have been buried in any of the subjacent 

 deposits. Boulders of trap rocks are by far the most common, but 

 with them are many fragments of sandstone, limestone, and even of 

 coal, and a few also of primary rocks. I have found the latter over 

 every part of the coal-field, and far up the sides of the transition 

 mountains that bound it on the south : even in the centre of that 

 chain, in the valley of the Tweed, boulders of primary rocks, though 



