1 82 FRA GMENTS F SCIKNCE. 



out without dislocation and fracture; and 'this conclusion 

 gains in probability when we consider the foldings, contor- 

 tions, 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 dislocation. 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 upheaval 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 diameter, 

 and let us suppose, in the first instance, the circumference 

 of this circle to remain fixed, and that the elevation was 

 confined to the.space within it. The upheaval would throw 

 the crust into a state of strain; and, if it were inflexible, 

 the strain must be relieved by fracture. Crevasses would 

 thus intersect the crust. Let us now inquire what propor- 

 tion the area of these open fissures is likely to bear to the 

 unfissured crust. An approximate answer is all that is here 

 required; for the problem is of such a character as to render 

 minute precision unnecessary. 



No one, I think, would affirm that the area of the 

 fissure's would bte one-hundredth the area o'f the land. For 



