Glaciers in Scotland in Ancient Times* 29 



(bords) of glaciers, we meet with blocks of all dimensions pell- 

 mell, some completely angular, others more or less rounded, 

 with pebbles of every size, and even sand of extreme fineness, 

 or in the state of finely'triturated clay. Schists, limestones, and 

 particularly marls, are of all rocks those which disintegrate 

 the most rapidly. These last, instead of being transformed 

 into rounded pebbles, become a soft paste, forming a bed of 

 mud under the glacier, or dikes of clay on its sides.'' {Etudes 

 sur les G lacier s^ p. 101.) There are no marls here, but the 

 schists, which are partly micaceous, partly chloritic, pro- 

 bably disintegrate with considerable ease, and much of what 

 were fragments at first may now be in the state of clay. 



Fig. 4 sliews the profile of the terraces, or their form in 

 a cross section ; op the natural declivity of the ground ; e d 

 the thickness of the terrace, or its depth at right angles to the 

 declivity, which varies from 10 to 20 feet. The top generally 

 slopes forward as at x, but sometimes it forms a cavity 6, 8, 

 or 10 feet deep, as at y. The breadth of the terrace, measured 

 parallel to the declivity, sometimes exceeds 100 feet. It will 

 be seen that the form of the terraces has a very close resem- 

 blance to that of lateral moraines, as shewn in fig. 2, al- 

 lowance being made for the eff^ects of meteoric action during 

 many thousand years. If this explanation of their origin is 

 objected to, it will not be easy, I think, to account for their 

 existence. Their marked deviation from the horizontal posi- 

 tion will not permit us to suppose that they were deposited 

 by water. 



I was unable to trace them farther north than to a point 

 behind Mr Napier's villa. Their absence from the part of 

 the hill marked a seems to be well accounted for by its low 

 elevation (600 feet), and the slightness of the declivity on its 

 upper part. For moraines derive their materials from ledges 

 or scarps of rock high above the glacier. If the rock is naked, 

 fragments are detached from it by frost, rain, and wind ; if 

 covered with snow, the snow slides down occasionally in 

 avalanches, bringing debris with it. The moraines first ap- 

 pear under the part 6, which is 900 feet high, and steeper in 

 the sides than a, and they are continued under c, which is 

 more than 1200 feet high. That the higher ones, 1 and 2 



