518 THE GLACIAL LAKE AGASSIZ. 



liave a remarkable parallelism, which probably indicates a similar sequence 

 of events on the opposite sides of the North Atlantic.^ 



When the building' up of a great range of mountains ensued, which 

 may have been initiated and accelerated by the repeated depressions imder 

 ice weight and consequent transfers of the earth's deformation from one 

 region to another, the accumulated stress in the earth's crust with develop- 

 ment of immense lateral pressure would be diminished below the limit of 

 its competency to cause glaciation. 



It seems probable that the rate of the earth's contraction has been 

 somewhat uniform throughout the vast ages known to us liy the researches 

 of geology ; but the corrugation of the earth's surface in mountain-building 

 has been much more rapid in some epochs than in others, and between the 

 times of formation of great moimtain ranges there have been long intervals 

 of quietude.- The slowly progressing contraction of the globe has been 

 uninterrui^ted, and in some way the cooled outer part of the crust which 

 has not shared in this diminution of volume has been able to accommodate 

 itself to the slu-inking inner mass. As stated in previous pages, this has 

 probably resulted in distortion of the earth's form, both of the whole thick- 

 ness of the crust and of the plastic or molten interior, within moderate 

 limits, during the periods of quiet, until so much lateral pressure has been 

 accumulated as to compress, fold, and uplift the strata of a mountain range. 



In attributing the severe climate of the Glacial period to great uplifts of 

 the areas glaciated through such deformation preparatory to the process 

 of mountain-building, it is distinctly implied that Pleistocene time has been 

 at first exceptionally marked by such broad crustal movements and has 

 since gained comparative rest from the lateral stress to which they were 

 due by equally exceptional plication, uplifts, and faults, in the birth and 

 growth of mountains. Further, it is implied also that stress in the earth's 

 crust had been gradually increasing through long previous time, while the 

 processes of mountain-building failed to keep pace with contraction, but 



'E. D. Salisbury, Am. .lour. Sci. (3), Vol. XXXV, pp. 401-407, May, 1888. James Geikie and T. C. 

 Chamberliu, The Great Ice Afj;e, third ed., 1894 ; Journal of Geology, Vol. Ill, pp. 241-277, April-May, 

 1895. Warren I'pham, Am. Naturalist, Vol. XXIX, pp. 235-241, March, 1895 ; Am. Geologist, Vol. XV, 

 pp. 273-295, May, 1895. 



^Dana's Mauual of Geology, 3d ed., p. 795. Prestwich'a Geology, Vol. I, Chapter XVII. 



