238 FKAGMENTS OF SCIENCE. 



Their present elevation above the sea is due to one of 

 those local changes in the shape of the earth which 

 have been of frequent occurrence 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 consider 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 dislocation. Fis- 

 sures 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 pro- 

 duced 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 conclu- 

 sion 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 as- 

 sume the elevation to be general that a swelling out 

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



