80 TRANSFORMATIONS OF ROCK-MATTER. 



rocks have undergone the greatest amount-of metamorphism 

 or internal mineral transformation. So great, in many in- 

 stances, has this change been, that stratification is rendered 

 indistinct, fossils obliterated, new minerals evolved in the 

 mass, and the rocks rendered so crystalline and homogene- 

 ous that it is difficult to determine whether they are really 

 of sedimentary or of igneous origin. Normally speaking, 

 between the most recent and most ancient rocks there will 

 be every gradation of metamorphism, and it is to this pro- 

 cess that the geologist must learn mainly to ascribe the 

 different aspects and textures that prevail among the rock- 

 formations of the globe. The atmospheric, aqueous, and 

 igneous forces may destroy the rocks in one region and 

 re-form them in another, but metamorphism is the sure and 

 silent agency by which they are compressed, solidified, 

 crystallised, and converted into other and other aspects. 

 ~No rock be it shale, sandstone, limestone, coal, iron- 

 stone, lava, or greenstone remains for ever the same. It is 

 incessantly, however slowly, passing on to other and newer 

 aspects, and metamorphism is the great wizard-power by 

 which the transformations are effected. A sandstone, how- 

 ever soft and granular now, will in time, and under the fit- 

 ting conditions, be converted into a crystalline quartzite, an 

 earthy limestone into a saccharoid marble, a tender and 

 bituminous coal into a hard and nameless anthracite, a 

 porous lava into a close-grained greenstone or basalt, and 

 a greenstone itself, by farther change, into a large-grained 

 crystalline granite. When once the operations of metamor- 

 phism are fully understood, the geologist has a key to much 

 that is puzzling and perplexing in his science j and not till 

 the efficacy of these is everywhere admitted can he be said 

 to have adopted the right methods for the solution of his 

 problems. 



As the oldest rocks have undergone the greatest amount 



