Geological Society. 519 



No great river follows this course, but it is marked everywhere 

 by lakes or ponds, which afford shell-marl, swamps, and peat-mosses, 

 commonly surrounded by ridges of detritus from fifty to seventy 

 feet high, consisting in the lower part of till and boulders, and in the 

 upper part of stratified beds of gravel, sand, loam, and clay, which 

 in some instances are curved or contorted ; the form of the included 

 spaces is sometimes oval, sometimes quadrangular. No organic re- 

 mains have been found in the surrounding ridges, but they resemble 

 greatly in form the mounds of detritus which may once have con- 

 stituted the lateral, transverse, or medial morains of a great glacier. 



Mr. Lyell compares the chain of this part of the Grampians to 

 the Alps, the parallel chain of the Sidlaw hills to the Jura, and 

 Strathmore to the great valley of Switzerland ; and the resemblance, 

 he says, is increased by the occurrence in Strathmore and on the 

 Sidlaw hills of blocks derived from the Grampians. He is of opinion 

 that the agency of ice moving upon dry land may account for many 

 appearances which are inexplicable on any other hypothesis, and that 

 this theory must not be rejected because it fails to remove at once 

 every obscurity ; especially as various other geological causes, such 

 as oscillations of level in the land, the temporary submergence of 

 portions of it during the supposed glacial period, and the action of 

 drift-ice, may all have co-operated with glaciers to produce the boul- 

 der formation. He also hints, that the glaciers of Switzerland, being 

 situated eleven degrees further to the south, can present but an im- 

 perfect analogy to the state of things which may once have prevailed 

 in Northern Europe ; it is to Sandwich or Kerguelen's Land, or to 

 South Georgia, and other regions of the southern hemisphere cor- 

 responding in latitude to Scotland and England, that we must look 

 for instruction ; for these southern and antarctic lands are buried 

 summer and winter beneath perpetual snow, which reaches even to 

 the sea-coast, and yet in the case of South Georgia this perpetual 

 snow is distant only nine hundred miles from Terra del Fuego, a 

 country placed in the same latitude and yet clothed with luxuriant 

 forests. Assuming therefore that the Grampians, Alps, and Jura, and 

 all Scandinavia, were once permanently overspread with snow, he 

 thinks we cannot therefore conclude that the whole globe between 

 the fortieth parallel and the poles was invested simultaneously with 

 a sheet of ice, nor even that the general climate of the whole earth 

 differed materially from that prevailing in our own time. 



Mr.Murchison, in an admirable chapter (c.39.) of his Silurian Sy- 

 stem, on the Position and Mode of Transport of Boulders which occur 

 in the Northern Drift, has stated good reasons for believing that such 

 a change of climate may have taken place at the epoch of the trans- 

 port of erratic blocks as permitted the formation of icebergs on the 

 shores and rivers of Cumberland, Scotland, and Ireland; which be- 

 ing drifted southwards, strewc-d their load of large stones and gravel 

 over the bottoms of then adjacent seas. He also quotes with appro- 

 bation tlie ingenious imagination by Mr. C. Darwin, of a proportional 

 distribution of the land and water in central and northern Europe, 

 very different from the present, and under which the southern jmrt 



