164 Proceedings of the Royal Physical Society. 



preserved at 1500 feet above the sea ; the highest boulder- 

 striae occur at an elevation of 1400 feet. The lowest of each 

 are at the coast line. There are tracts also which these two 

 kinds of glaciation agree in registering as debatable ground, 

 — where the ice passed now in one direction and now in 

 another. 



The north of England boulder-clay might with much truth 

 be described as one great striated pavement} 



Glaciation, however, bore by no means equally upon all 

 parts of the till. Ir certain hollows and notches of the 

 surface — in many of the narrow preglacial stream-channels, 

 for instance, which the ice crossed at right angles, the till 

 found a secure lodgment, and could remain undisturbed. 

 During the formation of a new reservoir for the Newcastle 

 water-supply near ChoUerford, the preglacial ravine of the 

 Dry Burn, a feeder of the North Tyne, was excavated to a 

 depth of 26 feet below the level of the modern stream. The 

 stiff till that had occupied it was full of boulders, many of 

 them having the characteristic smooth lobe-shape. These 

 boulders were lying as if hustled-in in the passing, and their 

 axes and striae were disposed at random. This old ravine lay 

 at right angles to the line of ice-movement. 



For several reasons also it is more difficult to obtain good 

 glacial evidence from boulders among the drirt at high levels. 

 The high level drift is often raw material ; the sections of it, 

 too, are increasingly obscure as we ascend. It is on the open 

 and level country, where the till was well worked up, and 

 the ice had a steady purchase or mechanical advantage over 

 the surfaces upon which it moved, that boulder-glaciation is 

 at its best. 



Pavement- Boulders near Edinhurgh. 



This was the case in the low grounds near Edinburgh. 



The accompanying small map represents sixteen sets of 

 boulder- striae in this neighbourhood. Three of them are 

 Maclaren's original observations of the year 1828; five of 

 them have been recorded by Mr Milne Home ; two represent 



1 The term pavement-houldcr which I find it convenient to employ, may- 

 be viewed in this wider sense. 



