102 ALPINE FLOWERS [PART I. 



arbitrary and accidental. They, like everything else in Nature, 

 form part of a plan. Hence a particular class of form is the 

 result for each rock of this purely mechanical action of the 

 weathering agent. In the case of quartzite, for instance, the 

 fracture is " conchoidal," or shell-shaped, concave and wavy; 

 this, on a large scale, gives rise to peaks with somewhat hollow 

 sides and ridged with sharp serrated edges. 



This may serve as an example of simple weathering on a 

 homogeneous, hard, and practically insoluble rock. Let us see 

 what takes place with more complex rocks, of which granite 

 may serve as a representative. This rock is made up essentially 

 of three minerals quartz, felspar, and mica in various propor- 

 tions. Now here the water with its carbonic acid will act not 

 only mechanically, as in the case of quartzite, but as a powerful 

 solvent and disintegrator. The fissures in granite are large and 

 continuous, taking the form of immense joints, which cross and 

 recross each other, often, but not always, in a regular manner ; 

 but besides these larger lines of weakness, which affect the 

 whole rock, there are those minute lines which separate the 

 constituent minerals from one another. Into all these the 

 water trickles, decomposing the granite k along the joints and 

 cracks, "widening them, and rounding off the angles of their 

 intersections, and ultimately only the harder masses, or the 

 hearts of the blocks defined by the joints, remain as solid 

 crystalline granite ; some though little of the quartz is dis- 

 solved away by the water ; the iron," which is usually present 

 in small quantities in granite, " becomes oxidized and weakens 

 the rock ; but it is chiefly the felspar that is decomposed by the 

 action of carbonic acid, its alkalies are removed, and its residue 

 is washed away in the form of fine china clay. . . . The quartz 

 crystals remain as sand ; the mica remains, but is less observ- 

 able, and is partially decomposed." (Professor Eupert Jones.) 

 It is by processes such as that described, that the many fantastic 

 shapes assumed by granite rocks have been arrived at, whether 

 they be those of the curious balanced "Logging" stones of 

 Cornwall or Brittany, the bare rounded tors of Devon, or the 

 grey sterile mountain-tops of Aberdeenshire. All felspathic 



