Febbtjabt 1, 1807] 



SCIENCE 



167 



Le Conte, mountain ranges have been only 

 exceptionally developed by geantielinal 

 uplifts of the earth's crust. A mountain 

 range, in general, has its birth in a geo- 

 syncline— a downward folding of the crust, 

 forming a trough, in which sedimentation 

 goes on pari passu with the subsidence. 

 At length, after long ages of subsidence 

 and sedimentation, the strata in the trough 

 are crushed together into alternate anti- 

 clines and synclines, or one part is forced 

 over another in = great thrust faults, while 

 slaty cleavage and more decided meta- 

 morphism may be produced. The mountain 

 range thus produced Dana called a 'syn- 

 clinorium, ' while he suggested the name 

 'anticlinorium' for a mountain range 

 formed by a permanent geantielinal eleva- 

 tion. Apparently the actual history of 

 most mountain ranges is complex. The 

 Appalachian range, for instance, was 

 formed as a synclinorium at the close of 

 the Paleozoic, degraded nearly to base-level 

 in Mesozoie time, and again elevated by a 

 broad geantielinal movement early in Ceno- 

 zoic time. It represents, therefore, in its 

 complex history, Dana's two types of the 

 synclinorium and the anticlinorium. 



There are unquestionably weak points in 

 the theory of mountain-making as devel- 

 oped by Dana and Le Conte; and, in our 

 ignorance of the conditions in the interior 

 of the earth, and of the forces there in 

 action, it ill becomes us to be dogmatic; 

 but the contractional theory seems worthy 

 of provisional acceptance as the most 

 plausible explanation of orogenie move- 

 ments yet suggested. 



in. GLACIAL GEOLOGY 



Surely no part of the world affords bet- 

 ter opportunity for the study of glacial 

 geology than America. Its ice sheet, four 

 million square miles in area, far exceeds 

 any of the ice sheets of the Old World. 

 The imbricated sheets of till in the Missis- 



sippi Valley afford clear evidence of the 

 complex series of glacial and interglacial 

 epochs. The driftless islands in the vast 

 area of till, and the interlobate moraines, 

 show the division of the marginal portion 

 of the ice sheet into lobes determined by 

 the topography. The old beaches along 

 the shores of the Great Lakes, the living 

 Niagara, and the various extinct Niagaras, 

 record the stages of the melting of the ice. 

 The Malaspina Glacier affords illustrations 

 of the formation of eskers and of other 

 phenomena which must have marked the 

 stagnant margin of the waning ice sheet. 

 Surely our country affords most favorable 

 conditions for the study of the history of 

 the Glacial period. 



It is a curious fact that the first pub- 

 lished suggestion of the agency of ice in 

 connection with the drift came from a cot- 

 ton manufacturer in Connecticut, Peter 

 Dobson by name. In the American Jour- 

 nal of Science, in 1826, he gives a very 

 clear and satisfactory description of the 

 glaciated boulders observed in the drift, 

 and gives as his conclusion: "I think we 

 can not account for their appearances un- 

 less we call in the aid of ice along with 

 water, and that they [the boulders] have 

 been worn by being suspended and carried 

 in ice, over rocks and earth, under water." 

 It was his idea that these boulders were 

 lifted from the bottom of the sea by sheets 

 of anchor ice. This theory was certainly 

 more satisfactory than most of the theories 

 in vogue before that time, and more satis- 

 factory than many of the opinions held at 

 a later date. 



The credit of the introduction and cham- 

 pionship of the glacier theory of the drift 

 belongs, not to a native, but to an adopted 

 citizen of this country. Louis Agassiz 

 came to this country in 1846. In his early 

 home in Switzerland, he had already adopt- 

 ed the belief of Venetz and Charpentier in 

 the former great extension of the Alpine 



