Rev. 0. Fisher — Reply to Capt. Hutton. 65 



crust. Because in the case of an arch or dome part of the force of 

 gravity may be resolved in the direction of the curve of the arch or 

 dome everywhere, except at the crown ; and the conditions of equi- 

 librium depend essentially upon this fact. In the case of the earth's 

 crust, considered as a whole, such is not the case, for gravity is 

 everywhere perpendicular to the surface. Any small portion of the 

 crust, however, which has been already elevated (by any means) into 

 an anticlinal, is to some extent under the conditions of an arch or 

 dome, and may be partially supported as an arch or dome would be, 

 as I have particularly pointed out in my paper of 1869. 



The gist of my argument against Captain Hutton's main proposition 

 lies here. For if the portion of the crust supposed ready to expand 

 beneath newly-deposited matter were maintained, partly by forces 

 acting as the pressures act along an arch, — tliat is, partly upioards or 

 against gravity, — then, if the crust expands, an upward movement will 

 ensue; and this seems to be Captain Hutton's view. But if, as I 

 contend, the forces along the crust are horizontal, — that is, at right 

 angles to gravity, — expansion will not cause any direct upicard 

 pressure; and there will be, consequently, no tendency to raise the 

 portion of crust into a dome in preference to crumpling it into any 

 other form, which would equally suffice to relieve the pressure ; and 

 in which, by a due admixture of synclinals with anticlinals, the 

 centre of gravity of the portion as a whole would be raised only by 

 the small amount necessarily due to its deformation. 



(6.) I by no means consider that such crushing as I contemplate 

 is inconsistent with the formation of anticlinals. On the other 

 hand, I have expressly stated that horizontal pressure would break 

 up a layer of rock into " a series of synclinals and anticlinals inter- 

 spersed with faults." (By-the-bye, we hear little about synclinals 

 in Captain Hutton's theory.) Before we can argue upon the word 

 "crushing," we must define what it means when applied to matter 

 operated on upon so grand a scale as the earth's crust has been. 

 There ar,e but few (I will not say no) mountain sections in which I 

 should not call the strata " crushed." 



On the "contraction" theory, the upper strata of aqueous rocks will 

 have been subject to less compression, because they have experienced 

 the effects of only the later stages of contraction. They are not there- 

 fore subject, as Captain Hutton says, to the greatest, but to the least 

 compression. The difference of compression resulting from the 

 curvature of the surface in the upper and lower parts of the crust 

 would be absolutely inaj)preciable, on account of the small thickness 

 of that crust, compared to the dimensions of the globe. 



(c.) I think my reasonings referred to under this head are correct 

 upon the premisses. I did not make the sinking of an adjoining 

 area one of these. But the possibility of such an occurrence, and 

 its effect, is taken account of in other parts of my paper. 



(d.) In what I am told is my fourth argument, I do not recognize 

 myself at all. It is said to be that the specific gravity of the dis- 

 turbed rocks "ought" to be less than it was before. "This would 

 be the case with the rocks that caused the movement only while 



DECADE II. — VOL. I. — NO. II. 5 



