EARTH'S SURFACE METEORIC ABRASION. 75 



the Hnronian or Cambrian, the Cambro-Silurian, the 

 Silurian, the Carboniferous, and many of the newer 

 formations, that conglomerates and such accumula- 

 tions are not uncommon ; while in places they are so 

 massive and so frequent as to be characteristic of 

 geological groups. Meteoric abrasion could not have 

 formed such rocks ; glacial action may have had some- 

 thing to do with them ; but prior to their being deposited 

 as we now find them, the fragments and blocks of 

 which they are formed must have been tossed and rolled 

 about by the sea or some other large accumulation 

 of water. At the present day, in places on the coast of 

 our own little islands, we can study deposits accumu- 

 lating, that are identical in character with such rocks. 

 In the tropics the principal rocks that are being 

 formed by meteoric abrasion, are made up of more 

 or less fine materials, disintegrated by extreme heat, 

 and subsequently carried away by wind, or rain and 

 rivers, to be deposited in lakes or seas. 



If we look into the present conditions of Ireland it is 

 apparent that the growth of soil, except on the coast- 

 lines, must equal, if it does not exceed, the denuda- 

 tion by meteoric denudation. On the upper portions 

 of all but a few of the limestone hills, an envelope of 

 peat is growing which is yearly increasing, while two- 

 thirds of the lowlands are in a similar condition. Of 

 the rest of the country a half at least is under grass- 

 land or wood; consequently very little denudation can 



