PRESENT CHANGES IN THE EARTH. 103 



the feldspathic rocks, so that even the harder rocks are 

 not full proof against the chemical action of water. It 

 is from this action on these rocks that the silex is pro- 

 vided for the grains, and grasses, and other plants, in a 

 condition to be dissolved and carried up the plant in the 

 sap. Even the granite, of which man constructs his most 

 enduring monuments, is every where being slowly worn 

 away by this action, and thus ever furnishes its quota of 

 fertility to the soil in the alkali and clay that come from 

 its decomposing feldspar. 



187. Weatheriug. This is a term which includes, to 

 some extent, the mechanical action of water with its 

 chemical. The idea is that rocks, on exposure to the 

 weather that is, to rain and air, are more or less disin- 

 tegrated, and sometimes even changed in chemical con- 

 stitution, either at the same time or after the disintegra- 

 tion. This weathering is sometimes exhibited in a very 

 striking manner by ancient monuments. This is the case 

 with the Druidical monuments in the north of England, 

 which are constructed of a very hard rock called mill- 

 stone grit. Three monstrous pillars, called the Devil's 

 Arrows, having had the rain beating upon them for two 

 thousand years, are furrowed deeply all down their sides, 

 the furrows being deepest at their summits, and becom- 

 ing wider and less distinct toward the bottom. Crags 

 of rock too hard to crumble under the weathering often 

 present the same furrows. Where rocks are porous, and, 

 as we may say, loosely constructed, as are many sand- 

 stones, the disintegration of weathering goes on largely 

 and rapidly, and we have in such localities impercepti- 

 ble gradations from earth to solid rock. This may be 

 seen often where the rocks jut out from the soil, but 

 more especially in digging down through the success- 

 ive gradations of soil and crumbling rock to the hard 

 rock itself. The same weathering which disintegrates 

 the rocks does the same work among the fragments of 

 rock, small and great, in the soil, for both water and air 



