Ch. XII.] NATURE OF STRATIFCATION. 239 



planes, and has likened this accumulation to the filling up of 

 the furrows on the rippled surface of the sand hills, near 

 Calais, with sand drifted by the wind. And he adds, " We 

 must suppose that each thin seam was thrown down on a 

 slope, and that it conformed itself to the side of the steep 

 bank, just as we see the materials of a talus arrange them- 

 selves at the foot of a cliff, when they have been cast down 

 successively from above." Then comes the deduction : " We 

 think that we shall not strain analogy too far, if we suppose 

 the same laws to govern the subaqueous and subaerial 

 phenomena." To this we cannot assent, because, in the first 

 place, the analogy does not appear to be correct. A talus 

 certainly presents, in general, an inclined surface ; but, as 

 fresh materials fall, they are not equally spread over this 

 surface, for they are carried on by the force of gravity to the 

 lowest part of the inclined plane, where they accumulate to a 

 greater extent than in the upper ; so that, if we covered over, 

 or otherwise marked, the surface between each precipitation, 

 it would be found that the layers are not parallel, but fan- 

 shaped ; and the angle of the surface would constantly fluc- 

 tuate during the accumulation. The condition, then, of such 

 layers does not accord with those under consideration, and 

 the case would be still more dissimilar under water, for it 

 would require a current, or some moving power, to transport 

 the materials of which the inclined laminae are composed, to 

 the slope ; and, at an angle much less than that of 45 or 

 even 30, their heterogeneous constituents would be arranged 

 according to their specific gravities. And it cannot be argued 

 that the transported materials (the sand, slime, and shells) are 

 so light, that the moving power might have acted very gently, 

 for these layers sometimes consist of shingle, as at the light- 

 house near Happisborough. Indeed, Lyell himself has sub- 

 verted his own analogy ; for, when speaking of the sand hills, 

 he says, " When a gust of wind blew with sufficient force to 

 drive along a cloud of sand, all the ridges were seen to be in 

 motion at once, each encroaching on the furrow before it, 



