VII. 



ON THE MOVEMENTS CAUSED IN LARGE ICE- 

 FIELDS BY EXPANSION AND CONTRACTION, AS 

 ILLUSTRATIVE OF THE FORMATION OP ANTI- 

 CLINAL AND SYNCLINAL AXES IN GEOLOGICAL 

 FORMATIONS. 



By MONTGOMERY C. MEIGS. 

 (Prepared April, 1869. Read February 27, 1875.) 



Hearing the discussion of the National Academy upon the sec- 

 tiou of the Appalachian formations contributed by Mr. J. P. Les- 

 ley, N. A., I was led to recur to certain phenomena which were daily 

 presented to my observation during two severe winters spent at 

 Rouse's Point on the shores of Lake Champlain in latitude 45° N. 



The winters in that region are severe. The thermometer is 

 frequently below of Fahrenheit for days together. It seldom 

 descends below — 30°, but — 18° is a not uncommon temperature. 

 The lake is fed by streams which rise in the Adirondack and Green 

 Mountains, deriving their supplies from the heavy snows of those 

 ranges, where four feet of snow on a level is not uncommon. Its 

 waters are clear, cold, and still. No current exists to move the 

 ice, which is produced early and remains late. Its thickness, I 

 judge, averages about twenty-four inches. The lake is irregular 

 in form. Its shores and those of the islands it contains are gen- 

 erally I'ocky, with some beaches of drift gravel, sand, and boulders. 



While at night the thermometer descends to — 30°, during the 

 day the sun's rays, shining through a dry, clear atmosphere, have 

 considerable power. The ice, a two feet thick stratum floating 

 freely upon the quiet water, lies between the water always at 32° 

 and the air varying from -f-32° to — 30° and further subject to the 

 action of the direct rays of the sun. Its lower surface must 

 always retain the uniform temperature of freezing water or melting 

 ice ('-|-32°). Its upper surface may take any temperature between 

 -[-32° and approximately — 30°. As ice, when once formed, is sub- 

 ject to the same laws of expansion and contraction as other solid 

 bodies, the upper surface contracts under the low nocturnal tem- 

 perature, producing a tension which is suddenly relieved by ex- 

 tended cracks. On a frosty night the great ice fields, 125 miles long 

 and from 1 to 10 miles in width, are continually cracking with a 

 rushing or roaring sound, which is one of the striking natural 

 phenomena of this northern region. A crack sometimes starts 

 apparently at the feet of a traveller on the ice, and its rushing 



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