368 Dr, T. Sterry Hunt's Lecture— 



great mass of th.e earth, and, consequently, of the independence of 

 volcanic phenomena of any supposed theory of a fluid nucleus 

 within. Yet it is not the less true that we have in volcanic phe- 

 nomena a condition of things which recals sufficiently the state 

 which must have existed at the very commencement of solidification 

 upon our planet ; — that we have still evolved molten rocks, which 

 are very like what I suppose this first scoriaceous crust of the earth 

 must have been ; — that we have evolved from these volcanoes dif- 

 ferent gases and vapours such as must have floated over the surface of 

 the first formed and first solidified planet ; and they come in as 

 beautiful explanations of what I was endeavouring to explain— the 

 composition of this crust, for they are really the result of the melting 

 together of the successive interstratified and intermingled layers of the 

 earth's crust, and may represent,over very considerable areas, the mean 

 composition of the stratified rocks. When these become depressed, 

 so that they come within the action of the central heat passing up- 

 ward by radiation, then takes place the fusion, the melting together 

 of the limestones, of the clay, of the salt, of the gypsum, and of the 

 gault together with the sand, and there are produced these fused 

 scoriaceous masses which we call lavas ; and, at the same time, are 

 liberated enormous masses of elastic fluids and gases which produce 

 all the phenomena of volcanic eruption. However, in certain cases 

 where there is no disengagement of gases you have simply the 

 crystallization of the rocks — the conversion of them into what we 

 call granites, or gneisses, or mica-slates, and other varieties of crystal- 

 line rocks which form so often our great mountain chains. And we 

 have, morever, in the movements dependent upon this crystalliza- 

 tion, depression in one part and upheaval in another. We have 

 those movements which preserve the irregularity of the surface of 

 the earth, which prevent it from being entirely depressed beneath 

 the level of the sea and converted into one vast ocean. And here 

 we see coming up the old vexed question of the Neptunists and the 

 Plutonists. There are persons still living who recollect the con- 

 troversy which raged at the close of the last and the beginning 

 of the present century, and which in Germany and Edinburgh 

 raged with such virulence that the opposing parties were almost 

 broken up socially. You had the school of Werner or the Neptunists 

 on the one hand, and the school of Hutton or the Plutonists on the 

 other. The one endeavoured to create the earth entirely by water, 

 and the other as entirely by fire. In the light of modern chemistry, 

 I think we may now safely conclude, that the origin of the earth was 

 first an igneous mass, — that fire came in and did its work until a 

 cooling took place sufficient to allow of the precipitation of water, 

 and from that time the mechanical action of water, and the chemi- 

 cal action of water, and of acids and gases, were the principal means 

 in modifying the rocks at the surface of the earth, and it was only 

 when these became thickly accumulated, and depressed below a cer- 

 tain level, that they came again within the domain of Pluto, where 

 the igneous actions were again commenced, which produced those 

 igneous rocks which were confidently appealed to by the Plutonists 



