Metamorphism. 411 



That they have, however, in some cases, been produced by the 

 change or metamorphism of regularly stratified, rocks, and in 

 the very midst of such rocks — some underlying them and some 

 overlying — that certain parts of slates and such like rocks have 

 been converted, or metamorphosed into granites, while other 

 parts adjacent have not been more altered than slates generally 

 are, is rendered so probable by the study of actual rocks in the 

 field, that if not fully accepted as proved it must .still be 

 regarded as one of those matters ,to be expected, and of which 

 there is every probability. There are now many places described 

 in England, Wales, and Ireland where granites and porphyries 

 of various kinds fairly alternate with slates and other rocks, 

 where it is so utterly improbable that they can have been forced 

 in between those rocks after being once formed, and so certain 

 that they could not have been thrust in in a melted state, that 

 we are forced to the conclusion above stated, namely, that 

 granite also is nietaniorphic ; that like the rest it is due to 

 water rather than fire. 



The reader may be prepared to ask how it is that chemical 

 changes so energetic, transformations and replacements so 

 complete, and metamorphoses on a scale so gigantic are con- 

 sistent with the ordinary state of apparent tranquillity of the 

 interior of the earth. The rumblings of earthquakes, though 

 certainly not infrequent, are limited to very small area; the 

 eruptions of volcanoes are very much more limited, and are 

 altogether exceptional phenomena, occurring on a large scale 

 only once or twice in a century. But the changes we speak of 

 must be incessant, and their amount must be large. Their 

 effects are everywhere. 



We reply that the apparent repose of the earth is not real ; 

 that as the giant oak standing firmly rooted in the earth, and 

 for centuries unmoved by the fiercest storm, owes its apparent 

 uniformity of condition to changes incessantly going on within, 

 and to ceaseless currents of sap that circulate through its 

 whole tissue — that it only lives, and is strong, because of this 

 continual change and replacement that we call life ; so the 

 great old globe itself has its life, its fluids circulating through- 

 out, removing, replacing, modifying, and renewing. Every- 

 thing in nature is in perpetual circulation, and water passing 

 everywhere is the circulating medium. It is the earth's blood, 

 preserving life, replacing the old and worn-out material by new 

 material, separating that which has performed its work, and 

 putting it in the way of entering into new combinations, and 

 enabling it to come in once more as a useful element. 



But there is something besides, for the word life has a 

 different and a higher meaning. Vitality requires not only a 

 circulating fluid, but a certain energy, which in the animal we 



