Metamorphism. 413 



but all other rocks in all countries tell the same tale. There 

 are proofs of this, and illustrations of the mode of change 

 everywhere, and the great agency employed has certainly, in 

 most cases, been altogether unconnected with heat and igneous 

 fusion. The very oldest rocks, even those lowest in the series, 

 all speak by their nature, structure, and composition of other 

 rocks still older, all, without exception of the stratified series, 

 have been derived by the aid of water from the destruction of 

 some of yet greater antiquity. And amongst rocks of all ages 

 are the granites : in rocks of all ages are veins of greenstone and 

 such like mineral compounds. Were all these thrust up in a 

 melted state through the stratified rocks and amongst them, or 

 have they not rather been deposited where we see them in a 

 more quiet way by the help of water acting under favourable 

 conditions of temperature and chemical force ? These are im- 

 portant questions in modern geology. It is certain that granites 

 and porphyries are not all of the same date, but that some have 

 lasted little altered during whole geological periods, while 

 others have been elaborated in recent times. But so it is also 

 with slates, and schists, and limestones, for some of these are 

 new and some old, although the appearances hardly vary. There 

 is no great heat required for most of the changes, and, in fact, 

 many of them are absolutely inconsistent with the presence of 

 such an amount of heat as would produce fusion. 



On the other hand water and its known action afford the 

 only simple and intelligible explanation of a large class of phe- 

 nomena, and will explain the universal difference traceable 

 between recent deposits and those that have long been de- 

 posited, and have undergone change of position and exposure 

 to the causes at work beneath the earth's surface. Water and fire 

 are two important agents employed by nature, and both assist 

 in the same great work — that of inducing chemical and atomic 

 change. Both seem to produce, or at least to pave the way for 

 decomposition and re -combination. Each is powerful, and 

 opposite as they seem, both work together in the production of 

 •all great results in nature. Near the earth's surface, however, 

 water acting at moderately high and equable temperatures, and 

 under pressure, would seem to be nature's method of bringing 

 about the largest results, and this seems to be not only the 

 case at present, but to have been equally the case in the very 

 earliest times which geological investigation introduces to our 

 notice. The only clear and unmistakeable proofs of igneous 

 action that we possess are the modern lavas, and those ancient 

 sheets of lava called basalt, that have clearly been ejected in a 

 molten state, and have spread themselves in thin sheets over 

 the surface. These at all times seem to have been partial, and 

 on a small scale, and would appear to have few if any relations 



