INTRODUCTORY : THE GEOLOGICAL WORK OF GLACIERS. 5 



detrital material of Northeastern North America is destitute of any true 

 morainic character. Under the idea that, notwithstanding this fact, it has 

 had a glacial origin, and hence must once have had a structure analogous to 

 that of true moraines, much of it has been designated as " modified drift " ; 

 by which term it is meant to be understood that its real origin has been to 

 a certain extent masked by the action of water. 



Detrital material arranged in long linear accumulations, somewhat resem- 

 bling moraines, but partly stratified and differently situated with regard 

 to the topography of the country from I'eal moraines, are called sometimes 

 by the Swedish term "as" (plural asar). The Scotch word " kame " is very 

 closely analogous to as in its meaning, and it has been iised on this side of 

 the Atlantic, as well as on the other. As defined by J. Geikie, it includes 

 sands and gravels having a tendency to shape themselves into mounds and 

 winding ridges, which give a humraocky and rapidly luidulating outline to 

 the ground.* The peculiarities of the asar will be noticed somewhat in 

 detail, when describing the glacial phenomena of Scandinavia. 



The finer kinds of detrital material resulting from the wearing down of 

 the rocky masses are variously designated, and usually by terms not liable 

 to misconstruction. The quartzose portion of the rocks, especially the quartz 

 itself, yields slowly to degradation, and is not so easily reduced to the finest 

 condition ; argillaceous rocks, on the other hand, readily allow themselves 

 to be ground into the finest powder : hence we have sands, which are usually 

 chiefly quartzose, and clays, or finely triturated argillaceous material. Of 

 course sand and clay may become mechanically mixed with each- other, 

 and such mixtures are easily designated. The term '' alluvium," with the 

 corresponding adjective " alluvial," was originally used in opposition to dilu- 

 vium and diluvial as implying a less turbulent origin, and as indicating the 

 work of the present rivers, rather than of former larger and more general 

 fioods. When it is desired to define the different varieties of alluvial deposit 

 and limit them by names, it is not found to be an easy matter, and certain 

 terms have become quite generally adopted, but which are not capable of 

 precise definition. It is not easy, for instance, to draw the line between 

 "soil" and "loam," nor between "loam" and "loess," the latter being a 

 term which has of late years come into quite genei'al use, and including, as 

 characteristic features of the material thus designated, fineness and uniform- 

 ity of texture, and absence of any well-marked lines of stratification. Loess, 



* J. Geikie, The Great Ice Age, p. 228. 



