620 STKATIGRAPHICAL GEOLOGY 



The till is described as a very stiff clay full of stones and 

 boulders, the whole being so hard and compact that it often 

 weathers like a conglomerate. Boulder-clay of this kind occurs 

 up to heights of 1600 feet, and is sometimes over 100 feet thick, 

 being always thickest on the low grounds and thinning away on 

 the highland slopes. The stones and boulders found at any given 

 locality are principally derived from local rocks, and in the low- 

 land clays there are not many stones which have travelled more 

 than a few miles from their parent site ; most of the fragments 

 are smoothed and striated, and many are scratched all over, often 

 exhibiting five or six definitely striated surfaces. The local 

 character of the clay is also shown by its variations in colour. 

 Hugh Miller, sen., long ago remarked that red sandstones were 

 covered by red boulder -cky, the grey flags of Caithness by a 

 lead -coloured clay, and the coal-measures of the Lothians by a 

 bluish -black clay ; subsequent observations have shown that the 

 clays of these colours do not exactly coincide with the limits of 

 the formations from which they derive their tint, but slightly 

 overlap them in an outward direction. 



Thus, though the materials of this inland boulder -clay afford 

 evidence of a certain amount of transport, still its local character is 

 so strongly marked that " whatever may have been its mode of 

 production, it cannot have been carried from a distance, but must 

 have been formed on the whole in the districts in which it is found." 



In many places the hard till or boulder -clay above described 

 is covered by deposits of a more varied character, consisting of 

 stratified sand, gravel, and clay ; such deposits occupy large areas 

 in the central lowlands between the firths of Forth and Clyde. 

 Associated with these beds or stranded on bare hill -sides are 

 numerous large erratics or isolated boulders, which have usually 

 come from points to the north or north-west of the positions they 

 now occupy, and some have travelled distances of 50 or 60 miles ; 

 it is to be noted that such boulders rarely occur in the boulder-clay, 

 though they often lie on it, the travelled stones in the boulder-clay 

 being always of small size. 



Along the east coast, from Stonehaven to Peterhead, a very 

 different kind of boulder-clay is found; this is a reddish-brown 

 clay which contains broken marine shells, and often includes 

 seams of fine sand or laminated silt ; moreover, its materials appear 

 to have been derived from the southward, from the Old Red Sand- 

 stone districts in Kincardine and Forfar, a conclusion which is 

 confirmed by the occurrence of striae on the rocks below, pointing 

 from south-south-west to north-north-east. 1 * 1 Near Collieston and 

 Slains this clay rests on stratified sands and gravels which are more 



