JOINTS AS AFFECTING SCENERY. Si 



ducible from water, and arranged according to entirely different laws 

 from those which regulate deposits from cold water. It seems, at 

 first, almost inconceivable that materials of such various specific 

 gravity and chemical affinities should be either soluble at once in 

 heated water or capable of being introduced by this process at 

 different times ; but all the circumstances agree in claiming for 

 mineral veins a different origin from basaltic dykes, the igneous 

 origin of which is supported by the strongest possible arguments. 

 We shall, however, discujs the history and nature of mineral veins 

 more at large in a subsequent chapter, and shall then notice pheno- 

 mena concerning them which can with difficulty be explained in the 

 present state of our knowledge of chemistry. 



Exhibition of Useful Minerals. It is not only in the elevation 

 of continents, the varying height of mountains, the division of the 

 sea, and similar striking effects, that we see the utility of the com- 

 bination of subterranean igneous with superficial aqueous agency. 

 Every coalfield in the known world proves distinctly the utility of 

 even the minor dislocations, which in our imperfect language are 

 called " faults " in the strata. The universal effect of these " faults " 

 is to multiply the visible edges of the strata, by bringing them more 

 frequently to the surface, in consequence of which there is, in the 

 first place, greater chance of discovering useful minerals ; and, secondly, 

 greater facility in working them. 



Internal Structure of Rocfcsi 



Joints in Different Rocks. All rocks, whether stratified or not, 

 are naturally divided by -fissures into masses, which are of different 

 forms in dissimilar rocks, and pass in various directions, independent 

 the strata. The fissures or planes of parting between these 

 isses are called joints. Most frequently their direction ' is nearly 

 it right angles to the planes of stratification or bedding, where such 

 dst, and they divide the rock into cubical, rhomboidal, or prismatic 

 )rtions, blocks, pillars, or columns. It is owing to their various 

 lirection and frequency that different rocks assume such characteristic 

 ippearances, and may thus be often and readily distinguished when 

 3n at a distance. 



Some rocks have very numerous, approximate, and closed joints, 

 shale, some kinds of slate, and laminated sandstones ; in others, as 

 limestones, the joints are less frequent and more open. 



In coarse sandstones they are very irregular, so that quarries of 

 us rock produce blocks of all sizes and forms. From this cause, 

 irse sandstone rocks show themselves against or facing the sea, in 

 >recipitous valleys, or on the brow of hills, in rude and romantic 

 grandeur. The wild scenery of the Peak of Derbyshire, Brimham 

 Crags, and Ingleborough in Yorkshire, derive attractive features from 

 the enormous blocks of Millstone Grit ; and the magnificent rocks 

 which stand upon the hills and overlook the Vale of Wye, are com- 

 posed of a somewhat similar material 



VOL. L F 



