hy Mr. John Farey. 44? 



and convey to us, both the facts and the reasonings, through 

 the medium of your useful Magazine : recollecting, that the 

 tides which I have supposed, necessarily imply all the me- 

 chanical agency of water, which is consistent with the pe- 

 riodic time and circumstances of the satellite occasioning 

 them and giving impulse to the fluid ; and Mr. Carr will 

 not, I hope, fail to consider, and inform us, of the motive 

 forces propelling and directing his (( incessant operator" in 

 the excavation of valleys. The example of the immortal 

 Newton, in declining to attempt the definition of the cause 

 of gravity, to which neither he nor any one else have yet 

 found themselves equal, shall be my excuse, in not at- 

 tempting a conjecture on the manner in which the forces 

 were directed, which excavated the valleys; the facts of 

 many of them having been mechanically excavated, and 

 that none (comparatively speaking) of the displaced mate- 

 rials are now any where to be found, are, as I think, incon- 

 trovertible. 



Perhaps Mr. Carr, when he speaks of water having given 

 w mobility and transportation to such massive and diversified 

 materials, " as compose the strata, had not contemplated a 

 supposition, which forced itself upon my mind, after having 

 perceived the difficulties which his position involves, viz., 

 that each successive stratum in ascending the series, was 

 created since the animal or vegetable remains which it co- 

 vers, had completed their growth, and the deposition of 

 which stratum, or its precipitation from the superincumbent 

 fluid, perhaps, occasioned the successive extinction of these 

 organized beings. The universal prevalence of grains in 

 siliceous strata, suggests the supposition, as I think, that 

 something analogous to the formation of kail in a storm, 

 (in irregular crystals) took place during the precipitation of 

 silex, generally, in very minute grains ; but in the first or 

 Mill-stone Grit Rock (vol. xxxi. Plate II.) it is not uncom- 

 mon to meet with grains half an inch, and even in some cases 

 three quarters of an inch in diameter, having that smoothness 

 of surface, as to induce Mr. Whitehurst and many others to 

 describe these large siliceous grains as rolled pebbles, but 

 which opinion 1 never could see reason for adopting; the 



surface 



