Notices respecting New Boohs, 381 



consideration of the probable modes and processes of ice-action 

 in producing its clay and stones, and in grinding, rounding, 

 polishing, and scoring the latter (Chapters V. and VI.). Doubtless 

 the glacier, as is well known, could do all this ; but it is very 

 doubtful indeed if the boulder-clay was a persistent floor of any 

 glacier ; or that the stones were not all derived from the frozen 

 rocks of the valley giving off their debris from the sides to its 

 surface. No ice could tear solid blocks from the floor. Water 

 running beneath the glacier carries along abundant mud and sand 

 amidst the grinding pebbles of the so-called " moraine profoncle ; " 

 and, though some layers are lodged in hollows and quiet recesses, 

 the rest passes on towards the glacier's foot, wherever that may 

 be, in river, fiord, or open sea. These considerations^ as to 

 whether it v\as a persistent bed on the glacier's floor (quite 

 impossible), or accumulated at its foot by water, with or without 

 icebergs and ice-floes, necessarily affect the explanation of the 

 local occurrences and disposition of the Boulder-clay, also of its 

 recurrence after the existence of a land-surface, and of its occa- 

 sional fossil shells and other organisms. 



The physical evidences of ancient ice-sheets ("mers de glace") 

 affecting Scandinavia and the British Isles, and regarded as 

 having been more or less conterminous or continuous, are enlarged 

 upon, and PI. IX., opposite page 437, delineates the supposed 

 greatest extent of this glaciation. Whether, however, this con- 

 dition existed over the European area uniformly at one and the same 

 time, and how thick the main ice-sheet may have been, are points 

 not yet proved to the satisfaction of all. In this, as in some 

 other cases, the Author prefers to collate and use the ideas and 

 statements supporting his views, without reference to contrary 

 opinions. 



Stratified and unstratified beds associated with the Scottish 

 Till form the text of Chapters VII. to XIII. At page 89 allusion 

 is made to " gravel, sand, silt, mud, brick-clay, and peat " that 

 underlie the lower till, and to similar beds lying upon it and 

 covered by the upper till. Some such deposits contain freshwater 

 fossils, and in some others there are marine shells. These " beds 

 below and in the till " are stated (p. 192) to indicate pauses in its 

 formation (though the lowest, being beneath, would seem to have 

 been formed previously !), and to have been due to ordinary 

 water-action. They are often of great interest, and have been 

 carefully examined by the geologists of Scotland wherever met 

 with in exposures, diggings, and borings. Froin them much has 

 been gathered as to the probable changes of fauna and flora under 

 different successive climates ("recurrent cold and warm periods ") ; 

 also of the former varying lines of rivers and lakes, and of the 

 conditions and features of the country during the formation of 

 these " glacial'"' and " interglacial " deposits. 



Chapters XIV. to XVII. treat of glacial deposits overlying the 

 till of Scotland, and their origin. These are the asar (escars) and 

 kames, ridges, mounds, and terraces of gravel and sand, due to 



