94 Correspondence — Mr. G. Poulett-Scrope. 



though of course this might happen. I do not think it had so done 

 in this case. 



T. G. Bonnet. 



Snt, — To the many explanations offered on Lithodomous Perfora- 

 tions, may I be allowed space to say, that in searching for facts in 

 Geology in the Fumess district, I met with a bed of slate-coloured 

 clay on the sea-shore, about half way between high and low water. 

 This clay was much bored, and the holes contained live Pholades, and 

 apparently at work. Suppose in time this clay becomes embedded 

 and changed into rock, and afterwards by some convulsion of 

 nature is thrown to the surface, may it not be possible for the action 

 of the atmosphere, rains, etc., to not only destroy the remains of the 

 original makers of the holes, but alter the appearance of them, and 

 the holes become useful winter homes for land snails. 



I have seen the rocks at Ormeshead and other places in Wales, and 

 more than 20 times those on Birkrigg, but after careful examination, 

 cannot see how the. explanations hitherto given fully account for the 

 borings. Samuei, Salt. 



Ulyerston, IQth January, 1870. 



TERRACES ON INLAND SLOPES. 



SiE, — I am glad to see, from the reply of Mr. Mackintosh in your 

 last number, that he no longer ventures to " assert" the marine 

 origin of these terraces, though he still " believes" that the greater 

 number of them are " Sea-worn." I will, however, suggest to him 

 that even such a modified "opinion," considering the importance of 

 the theory which it involves as to the very recent emergence of this 

 whole island from beneath the sea, requires an array of facts in its 

 support of which his book does not afford a single specimen. 



One word upon my " descent of silt theorj'," which Mr. Mackin- 

 tosh still cannot, in any case it seems, admit ; but which I look 

 upon as possessing a real interest to geologists who are speculating 

 on the causes which have modelled the existing surfaces, as showing 

 how large an amount of change the atmospheric forces, coupled with 

 that of gravitation, can produce within a very limited time. 



It is clear that Mr. Mackintosh will not yet comprehend that the 

 wash of rain on a plough-disturbed surface must, and does, carry 

 down by degrees a large amount of silt, or disintegrated soil, to 

 some lower level, where the force of the current sustains a check, 

 and the solid matters are deposited. If he will only look at a 

 recently ploughed slope, after a heavy rain-storm, he will see this 

 process exemplified in an unmistakable manner. He speaks of 

 " ridges artificially formed as boundaries between fields," as " distinct 

 from the terraces under consideration." Of course they are so, if he 

 refers to banks of earth raised high above the ground on both sides, 

 such as are common in Devonshire and some other counties. The 

 " terraces under consideration" are uniformly flat, or nearly so, on 

 the upper side, and rest on a steep bank fronting the lower side. 



