fluidity. In some rocks in Cornwall, and almost everywhere, we 

 find there are volcanic streams intermixing with all the harder 

 strata which originally existed. Although the surface of the earth 

 has been free from volcanoes in a given district for a time, yet 

 there has always been volcanic action near enough to force in 

 veins of fluid lava from time to time. It seems, therefore, that we 

 are entitled to say that we have always been near a great degree 

 of heat. We have been nearer than we are at the present time ; 

 but we are still near enough to experience a great deal in these 

 countries. Experiments have been made on the increase of 

 temperature as you go downwards, and the increase is one degree 

 of Fahrenheit sometimes in sixty, and sometimes one hundred feet 

 in depth. There is some uncertainty about it, but the increase of 

 heat is considerable. There is one mine in Cornwall I have been 

 in, in which I have walked in a stream of water actually scalding 

 to the legs. We know the quantity of water in various hot springs, 

 and there is a great display of volcanic action which certainly 

 came from great heat somewhere ; and in the intermediate ages 

 we can trace the formation of basaltic continents at no very 

 distant period. Since the valleys assumed their present shape in 

 the centre of France, they have been choked up with basaltic 

 matter, which you can trace to the volcanoes from which it came. 

 In the former ages there has been much more heat than at present. 

 In later times there is a great deal shown in the ejection of fluid 

 volcanic matter among volcanoes. 



There is another thing in connection with that, of which I 

 speak with no great boldness, but yet to which I cannot deny 

 some importance — that is the change in magnetism. The subject 

 of terrestrial magnetism is one of the most obscure in the world; 

 nevertheless I think, looking at the direction in which it always 

 acts towards the colder parts, and tracing its general phenomena 

 it must be affected by thermal electricity; and I imagine that 

 this may be produced by the constant wear going on in some parts 

 of the interior of the earth, where the hot fluid lavas are wearing 

 away solid parts, or are consolidating themselves into solid parts — 



