290 FKAGMENTS OF SCIENCE. 



throughout geologic time, in some cases depressing the 

 land, and in others causing the sea-bottom to protrude 

 beyond its surface. Considering the inelastic character of 

 its materials, the protuberance of the Alps could hardly 

 have been pushed out without dislocation and fracture ; 

 and this conclusion gains in probability when we con- 

 sider the foldings, contortions, and even reversals in 

 position of the strata in many parts of the Alps. 

 Such changes in the position of beds which were once 

 horizontal could not have been effected without disloca- 

 tion. Fissures would be produced by these changes ; 

 and such fissures, the advocates of the fracture theory 

 contend, mark the positions of the valleys of the Alps. 



Imagination is necessary to the man of science, and 

 we could not reason on our present subject without the 

 power of presenting mentally a picture of the earth's 

 crust cracked and fissured by the forces which produced 

 its upheaval. Imagination, however, must be strictly 

 checked by reason and by observation. That fractures 

 occurred cannot, I think, be doubted, but that the valleys 

 of the Alps are thus formed is a conclusion not at all 

 involved in the admission of dislocations. I never met 

 with a precise statement of the manner in which the 

 advocates of the fissure theory suppose the forces to have 

 acted whether they assume a general elevation of the 

 region, or a local elevation of distinct ridges ; or whether 

 they assume local subsidences after a general elevation, 

 or whether they would superpose upon the general up- 

 heaval minor and local upheavals. 



In the absence of any distinct statement, I will 

 assume the elevation to be general that a swelling out 

 of the earth's crust occurred here, sufficient to place the 

 most prominent portions of the protuberance three miles 

 above the sea-level. To fix the ideas, let us consider a 

 circular portion of the crust, say one hundred miles in 



