292 



GENESEE FARMER 



Dec 



Geology. — The Glaciers of Switzerland. 



[From the N. Y. Farmer and Mechanic] 

 On Thursday evening, the 25th ult., the win- 

 ter course of lectures at the Brooklyn Institute 

 was opened by Professor Agassiz, whose talents 

 and scientific acquirements have so justly con- 

 ferred upon him a wide spread and enviable 

 reputation. He commenced by briefly describ- 

 ing the geological formation of Long Island, its 

 loose, irregular and unstratified sand beds, and 

 particularly its numerous boulders, which are 

 found in great abundance and variety all over 

 the island and its surrounding shores. 



He stated that they were of all sizes, and in geological 

 formation entirely (liHerenL from that of the general charac- 

 ter of the natural deposits of this region, or that farther 

 South, being composed of granite, gneiss, &e., &c., which 

 exactly resemble the formations found in the northern part 

 of this conlinenf, from whence they were evidently at some 

 very remote period inlroduced. This fact, he stated, had 

 been admitted, but the question has been asked. By what 

 means these immense masses of rock had been transported 

 so great a distance, and what power was put in requisition 

 to effect it ? 



This, he said, had been sometimes answered by suppo- 

 sing these vast bodies of rock to have been forced onward 

 by the power of the current at a period when the great 

 Northern Ocean swept over the whole continent, and with 

 its mighty deluge produced this singular arrangement — 

 This the lef.rned lecturer proved to be incorrect, from the 

 fact that all these formations occur with great irregularity, 

 — that they are unstratified, and marked in straight and 

 nearly parrallel lines and furrows, showing conclusively 

 that they were never deposited by, or smoothed and round- 

 ed in a body of moving water and sand, as in that case the 

 largest and more ponderous masses would be found at the 

 North and the smaller at the South ; and also that the 

 heavier and leas easily moved portions would tind their 

 place at the bottom and the smaller and lighter at the top, 

 the contrary of which is, however, the case. Another the- 

 ory that they were transported on Icebergs across the North- 

 ern Seas he considered equally fallacious. 



In order, however, to account for this singular phenome- 

 non, the Professor introduced the subject of the glacial the- 

 ory and endeavored to account for their presence here, by 

 supposing that they had been brought hither at some remote 

 period by glaciers which may have fornad in the northern 

 portion of this continent, where exist, as before mentioned, 

 rocks precisely of similar formation to those which are here 

 seen. In support of this theory he adduced the well known 

 fact that stones of immense size are seen in the vtoraiws (or 

 accumulations of earth that line the edges of the glaciers of 

 Switzerland,) of an entirely different formation from those 

 of the valley, where these stupendous fields of ine exist — 

 and which are conclusively proved to have been pushed 

 along by the slow but steady propulsion of the glaciers. 



The lecturer described in detail the topographical features 

 of that country, the climate, the mode in which the glaciers 

 are formed by the freezing of partially melted snow, the 

 deep fissures or crevices, &c., which, as a ten year's resi- 

 dent and constant investigator of the glacial phenomena he 

 was enabled to do with great accuracy and minuteness. 



Professor A. here described the two principal mountain 

 ranges of the country, the Jura and the Alps ; the former 

 elevated about 1,(lOO and the latter towering to the height 

 of 11,000 to 13,(100 feet above the waters of Lake Neufcha- 

 tel, leaving an intermediate valley of about 60 miles in 

 extent, a section of which is given in the annexed diagram. 



A)/ 



Jura 4,000 

 feet high. 



Valley of Switzerland about I ^Ips 13,006 

 60 miles in extent. \ feet high. 



The Professor here desired to correct a ver5^ommon 

 error into which travellers were frequently betrayed, viz : 

 that of confounding the sjiow mountains with the glaciers ; 

 the former being merely immense masses of loosely formed 

 snow, while the latter, the glaciers proper, consisted of ics- 

 lields of immense size and depth formed in the valleys, 

 sometimes to the thickness of 500 to 600 feet. The follow- 

 ing diagram illustrates, seclionally, one of the glaciers be 

 tween the lofty peaks of the Alpine range. 



1,100 feet high. \ Ice 500 feet thick \ 1,500 feet high. 



The glaciers as they are formed and forced onward down 

 the mountain declivities and through the valleys, are cov- 

 ered with immense masses of boulders, some of which are 

 of astonishing magnitude, and which have been detached 

 and carried down the precipitous sides of the mountains 

 with the snow as it melted, and which during the day time 

 in the summer are constantly moving over the inclined sur- 

 face of these glaciers, rendering it exceedingly dangerous 

 to attempt their exploration, except early in the rhorning 

 before they become loosened by the warmth of the sun. 



These ice fields or glaciers generally terminate abruptly 

 as in the following diagram, which represents a small por- 

 tion of the glacier with its terminal slope, a representing 

 the mountain declivity, b the glacier 600 feet in thickness 



/ 



at the foot of the rocky declivity and 300 at c where it ter- 

 minates. This was demonstrated by actual measurement 

 and careful observation, and will give a general idea of the 

 glacial formation existing in the valleys. The ice forming 

 these glaciers has not the appearance of common ice, — is 

 not stratified, but being the filtration of water through the 

 snow masses of the mountains during the summer, inter- 

 mingled with the snow itself, it forms a granulated rnass of 

 frozen water and snow, and by the continued repetition of 

 this process the valleys are covered with a solid mass of 

 ice, while the snow remains loose on the mountains. These 

 immense bodies, or ice lakes, are forced forward by the 

 accumulated force from the slope of the mountains over the 

 face of the valley, until a slight descent occurs and then 

 the inequality of surface from the more sudden depression 

 causes fissures or crevices in the mass, as seen in the follow - 



Surface of the Valley. 

 During the summer the action of the sun on the surface 

 of these vast ice plains melts the parts most exposed to its 

 rays, and forms rivulets of several hundred yaros in extent ; 

 these rivnl'ls on meeting one of these fissures, the water is 

 precipitated over their crystal brink, forming the mo.st beau- 

 tiful cascades. Of these the Professor gave a glowing and 

 animated description, in a style simple, impressive, and 

 peculiarly happy. 



El 



In the above diagram a represents one of the above de- 

 scribed rivulets as i;. passes over the surface of the glacier 

 and falls into the fissure h, some 300 feet in depth. 



The Professor hero remarked that these fissures so fre- 

 quent and beautiful in the summer, are exceedingly danger- 

 ous in the winter, being frequently covered by a few fo©S 



