182 FRAGMENTS OF SCIENCE. 
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 bo 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 
fissures would be one-hundredth the area of the land, For 
