254 KECOKD OF SCIENCE FOR 1887 AND 1888. 



iiate pre-existing irregularities of surface, certainly by nioraine-build- 

 iug and probably by basin-cutting, aud must therefore be set apart as a 

 unique agent in tbe modificHtion of tbe external configuration of the 

 globe. The study of living glaciers was commenced many years ago by 

 reasou of the novelty of the subject and the paradoxical behavior of an 

 apparently rigid substance when accumulated in large mass ; but it was 

 soon ascertained that glaciers are among the most potent of the geologic 

 ageucies, and during recent years they have been studied chiefly with 

 the object of interpreting the frequently obscure records of glaciation 

 during past ages. 



Among the most important researches ui^on modern glaciers made 

 during recent years are those of Hoist upon the great mer de glace of 

 central Greenland, which have recently been summarized by Lindahl.* 

 These researches are of special value to students of the glacial phenom- 

 ena of America, since a considerable part of the mer de glace of Green- 

 land apparently occupies plains comparable in general features with 

 those of the Upper Mississippi Valley and the valley of the Great Lakes, 

 while most of the glaciers hitherto studied are constricted ice streams 

 flowing in mountain-bound valleys, whose behavior is determined 

 largely by the conditions these valleys impose. In the mountainous 

 parts of Greenland, as in the Alps and the northern Kockies the ice 

 is indeed crevasse- torn, diversified by bowlders and other debris de- 

 rived from projecting mountain tops, and sometimes broken by moulins, 

 into which small streams cascade ; but over the plains the ice is gener- 

 ally continuous, and free from rocky or earthy superficial deposits (other 

 than the kryokouite which has so long puzzled students of Greenland 

 geology), though sometimes intersected by considerable superglacial 

 streams. Kryokonite was collected in considerable quantity by Hoist, 

 carefully examined, and found to contain nothing but the ordinary com- 

 l)onents of non-eruptive crystalline rocks in finely comminuted condi- 

 tion — quartz, orthoclase, plagioclase, two or three varieties of mica, horn- 

 blende, garnet, magnetite, and doubtful traces of titanite and epidote; 

 but no metallic iron, nor the slightest trace of augite, olivine, or glass 

 were found. In short, the chemical composition and mechanical consti- 

 tution or kryokonite of Greenland is almost exactly identical with that 

 of the loess so extensively developed in aud along the flanks of glaciated 

 regions generally. Hoist's observations agree exactly with the conclu- 

 sion previously reached by most American students of the loess, i. e., 

 it is the finest flour of tbe ice-mill, which was swept into the glacial 

 streams, and slowly deposited in rivers, lakes, and morasses as the flow 

 became sluggish or ceased. 



Another notable study of living glaciers has been made by G. F. 

 Wright about Glacier Bay, in sonthern Alaska. t The observations 



* Am, Natunilist, 1688, vol. xxii, pp. 589-98, 705-13. 

 fAm. Jour. Sci. 1887, vol. xxxiii, pp. 1-18, 



