248 The Scottish Naturalist. 



ascribing the transport of erratics in that region (and by implica- 

 tion, the formation of the boulder-clays, &c, with which most of 

 these erratics are associated) to floating ice and sea-currents, Mr 

 Mackintosh has failed to furnish us with any " fossil evidence " 

 to show that Western England was under water at the time the 

 boulder-clays and erratics were being accumulated. He speaks 

 of cold and warm currents, but where do we find any traces of 

 the marine organisms which must have abounded in those waters ? 

 Where are the raised sea-beaches which must have marked the 

 retreat of the sea ? Where do we encounter any organic relics 

 that might help us to map out the zones of shallow and deep 

 water? The sea shells, &c, which occur in the boulder-clays are 

 undeniably remanies ; they are erratics just as much as the rock- 

 fragments with which they are associated. Similar assemblages 

 of organic remains are met with in the till of Caithness, where 

 shallow water and deep-sea shells, and shells indicative of genial, 

 and again, of cold conditions, are all confusedly distributed 

 throughout one and the same deposit. The same, or analogous 

 facts, are encountered in the Blocklehm of some parts of Prussia, 

 — marine and fresh-water shells occurring commingled in the 

 boulder-clay. Nay, even in the moraine profonde of the ancient 

 Rhone glacier, broken and well-preserved shells of Miocene and 

 Pliocene species appear enclosed in the tumultuous accumula- 

 tion of clay, sand, and erratics. And precisely similar pheno- 

 mena confront us in the glacial deposits of the neighbourhood 

 of Lago Lugano. Mr Mackintosh refers to the so-called " strati- 

 fication" of the boulder clay, as if that were a proof of accumu- 

 lation in water. But a rude kind of bedding, generally marked 

 by differences of colour, and sometimes by lines of stones, was 

 the inevitable result of the subglacial formation of the boulder- 

 clay. The " lines of bedding" are due to the shearing of the 

 clay under great pressure, and may be studied in the boulder- 

 clay of Switzerland and Italy, and in the till not only of the 

 Lowlands but of the Highlands of Scotland. Occasionally the 

 " lines " are so close that the clay sometimes presents the appear- 

 ance of rude and often wavy and irregular lamination — a section 

 of such a boulder-clay reminding one sometimes of that of a 

 gnarled gneiss or crumpled schist. And these appearances may 

 be noted in boulder-clays which occupy positions that preclude 

 the possibility of their being marine — as in certain valleys of the 

 Highlands, such as Strathbraan, and in the neighbourhood of 

 Como in Italy. This " lamination " is merely indicative of the 



