34 . Revieivs — Prof. N. S. Shaler — On Glaciers. 



explosions. Thirdly follows an influx of water from the underlying 

 sedimentary or other strata lying at greater depths into the ducts of 

 the volcano ; and, lastly, as these subterranean bodies of water are 

 thus converted into steam and expelled, the exhausted strata then 

 serve as a channel to an influx of sea-water into the volcano. 

 A point is finally reached when, owing to the cessation of the 

 powerful shocks and vibrations, and the excessive drainage of the 

 strata, the flow of the lava is effected quietly, and so continues until 

 another equilibrium is established and the lava ceases to escape. 



lEa :e ^T iiE -^w s. 



Illustrations of this Earth's Surface. Glaciers. By Prof. 



N. S. Shaler and W. M. Davis. 4to. pp. 198; 26 Plates. 



(Boston, 1881 : J. Osgood & Co.). 

 ri^HIS volume, which, according to the preface, is designed for 

 _L students, is presented to us with such a luxury of appearance, 

 and wealth of illustration, that only an affluent publishing house could 

 display. It forms the first of a series destined to jDortray the actual 

 features of the earth's surface under the action of geological agencies 

 by means of sun-pictures, together with an explanatory commentary. 

 The idea seems to us a happy one. In the present case advantage 

 has been taken of the admirable views of Swiss glaciers which are 

 to be had, owing to the enterprise of photographers, to place a 

 selection of them reproduced by the heliotype process before students 

 and the geological public; such being chosen as are most typical of 

 glacial phenomena. A few from India, Colorado, Norway, etc., are 

 also included. 



We do not imagine that the book will be confined to students in 

 the ordinary sense of the term ; it is suitable for and will doubtless 

 be found on many a drawing-room table. That large part of an 

 intelligent public who go again and again to Switzerland to revel in 

 the fascination of snow and ice scenery, will find in the views of 

 familiar glaciers what will bring the original scene vividly before 

 them, while in the letterpress and descriptions are pointed out 

 details which, perhaps, they did not notice, and of which, now, for 

 the first time, they see the meaning and importance. 



All know that a glacier moves ; their guides will not fail to tell 

 the tourist that, and, indeed, this fact was known to dwellers in the 

 mountains before scientific men paid any attention to it. In the 

 twelfth chapter the growth of our knowledge on the subject of 

 Glaciers is passed in review, for, to use the author's words, "the 

 student of nature will find that the best way into any science is 

 through the history of the discoveries that have made it a science." 

 In the opening chapter the physical phenomena are described ; in 

 the first place, those of the existing Swiss glaciers ; the grotto at 

 the lower end whence issues the stream of water, milky- white, from 

 the abraded mud, which has been the result of friction of the ice or 

 of stones imbedded in it like graving tools — the dirt bands, moraines, 



