152 GLACIATION OF SCOTLAND. [Oh. XTI. 



Forth, there is a form of hill to which Sir James Hall gave the 

 name of " Crag-and-Tail." Isolated ice-worn hills, or knolls, present 

 polished faces to the west and northwest in the district alluded to, 

 with rough declivities to the east and southeast, or where the tail 

 occurs. It is a common error, says Mr. Geikie, to suppose that this 

 " tail " consists merely of detritus, heaped up on the lee side of each 

 hill, for often it is composed in great part, like the west side or 

 " crag," of solid rock, but usually with a considerable covering of 

 boulder clay.'* 



According to Mr. T. F. Jamieson, on extending our survey of 

 Scotland we find many examples of such " crag," or natural escarp- 

 ments, facing the inland country, or that from which we may suppose 

 a mass of continental ice to have descended, whereas the " tail " or 

 mound of sand, and boulders, occupies the seaward side. It has also 

 been remarked in Scandinavia that abrupt protuberances and out- 

 standing ridges of rock are often polished and furrowed on the side 

 facing the region from which the erratics have come (usually on the 

 north side in Norway) ; while on the other, or " lee side," such super- 

 ficial markings are wanting. There is usually a collection on this lee 

 side of boulders and gravel, or of large angular fragments. In expla- 

 nation, we may imagine that the north side was exposed, when still 

 submerged, to the action of icebergs, and afterwards, when the land 

 was rising, of coast-ice, which ran aground upon shoals, so that there 

 would be great wear and tear on that exposed side, whereas on the 

 opposite or south slope, gravel and boulders might accumulate in a 

 sheltered position. 



The facts above alluded to, and other characteristics of the Scotch 

 drift, led Mr. Jamieson to infer, first, that in the early part of the 

 •glacial period Scotland stood much higher than at present, so that 

 there was a general covering of snow and ice, which, as it slid down 

 to lower levels, polished the subjacent rocks, and swept off from the 

 surface most of the preexisting alluvium, leaving in its place till 

 and boulders in various parts. Secondly, that to this succeeded a 

 period of depression and partial submergence, when the sea advanced 

 and gradually covered the greater part of the country, when floating 

 ice abounded, and when some marine drift with arctic shells was 

 deposited. Thirdly, that the land reemerged from the water, and, 

 reaching a level somewhat above its present heights, became con- 

 nected with the Continent of Europe, glaciers being formed once 

 more in the higher regions, though the ice probably never .regained 

 its former extension.f After all these changes, there were some 

 minor oscillations in the level of the land, on which, although they 

 have had important geographical consequences, separating Ireland 

 from England, for example, and England from the continent, we need 

 not here enlarge. 



* Glacial Drift of Scotland; Glasgow, 1863, p. 30. 

 f Quart. Geol. Joura., 1860, vol. xvi. p. 370 



