262 Prof. Tyndall on the Conformation of the Alps. 



mit of the protuberance from a point on its rim to a point oppo- 

 site. Regarding* the protuberance as a spherical swelling, the 

 length of the arc corresponding to a chord of 100 miles and a 

 versed sine of 3 miles is 100*24 miles ; consequently the surface 

 to reach its new position must stretch 0*24 of a mile, or be broken. 

 A fissure or a number of cracks with this total width would 

 relieve the strain ; that is to say, the sum of the widths of all 

 the cracks over the length of 100 miles would be 420 yards. 

 If, instead of comparing the width of the fissures with the length 

 of the lines of tension, we compared their areas with the area 

 of the unfissured land, we should of course find the proportion 

 much less. These considerations will help the imagination to 

 realize what a small ratio the area of the open fissures must 

 bear to the unfissured crust. They enable us to say with cer- 

 tainty, for example, that to assume the area of the fissures to be 

 -jLjth of the area of the land would be quite absurd, while that the 

 area of the fissures could be one-half or more than one-half 

 that of the land would be in a proportionate degree unthink- 

 able. If we suppose the elevation to be due to the shrinking or 

 subsidence of the land all round our assumed circle, we arrive 

 equally at the conclusion that the area of the open fissures 

 would be altogether insignificant as compared with that of the 

 unfissured crust. 



To those who have seen them from a commanding elevation, 

 it is needless to say that the Alps themselves bear no sort of re- 

 semblance to the picture which this theory presents to us. 

 Instead of deep cracks with approximately vertical walls, we have 

 ridges before us running into peaks, and gradually sloping to form 

 valleys at angles which, I imagine, would average less than 40 

 degrees, many of them certainly not reaching 30. Instead of a 

 fissured crust we have a state of things closely resembling the 

 surface of the ocean when agitated by a storm. The valleys, 

 instead of being much narrower than the ridges, occupy the 

 greater space. A plaster cast of the Alps turned upside down, 

 so as to invert the elevations and depressions, would exhibit 

 blunter and broader mountains, with narrower valleys between 

 them, than the present ones. The valleys that exist cannot, I 

 think, with any correctness of language be called fissures. It 

 may be urged that they originated in fissures : but even this is 

 unproved, and, were it proved, would still make the fissures play 

 the subordinate part of giving direction to the agents which are 

 to be regarded as the real sculptors of the Alps. 



The fracture theory, then, if it regards the elevation of the 

 Alps as due to the operation of a force acting throughout the 

 entire region, is, in my opinion, utterly incompetent to account 

 for the conformation of the country. If, on the other hand, we 



