PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 473 



that beneath a thin crust, of forty to one hundred miles in thick- 

 ness, all is in a state of igneous fusion ; that volcanos are but 

 chimnics to this great furnace below ; and that whenever there 

 is a collapse of the earth upon the molten centre, these melted 

 rocks are thrown up and overflow the surrounding country. It 

 is probable that this theory is true, at least, in part. It may 

 explain some of the large volcanos of the globe, such as Hecla, 

 Vesuvius, Etna, Stromboli, and some in Central America. More 

 i-ccentiy there has been a purely chemical theory advanced, viz : 

 That all sedimentary rocks, which are recently formed by the 

 deposition of sand, gravel, and mud, at the bottom of the sea, 

 contain a greater or less amount of animal and vegetable matter; 

 that when these rocks begin to condense, to change from their 

 soft, muddy consistency to a hard material, heat is evolved which 

 is increased to such an intensity, ly means of the organic matter 

 in the deposit, that the soft, pulpy mass is molten in part, and 

 begins to bubble up and overflow. In favor of this last theory, 

 it is alleged that, in the neighborhood of all the active volcanos 

 of the globe, the rocks are those of the latest formation, and are 

 now undergoing that process of condensation, and all contain a 

 very large per centage of organic matter. Further, as we go 

 back in the history of the globe, every great geological forma- 

 tion, while it was undergoing the process of formation, had its 

 volcanos and its earthquakes. They are to be traced through 

 the cracks, radiating from a centre, precisely similar to those 

 now found in Italy, Sicily, and Central America, immediately 

 following earthquakes. On the plains of Illinois, Avhere the 

 coun.try appears perfectly level, for instance, we are able, by 

 accurate surveys, to trace a system of cracks of such a descrip- 

 tion. And it is almost certain that wherever a river flows, there 

 is an ancient fissure in the rocks underneath it, which has deter- 

 mined its direction. This is true, not only of the Mississippi, 

 the Susquehanna, the Alleghany, the Hudson, but even the little 

 streams that come down from the mountains, and are dry in the 

 summer season, all have their course determined by some fissure 

 in the rocks beneath. In California, where volcanos now bubble 

 up like lakes of molten mud, hot enough to roast an egg in a few 

 minutes, all the rocks are of recent formation. The same is true 

 of Oregon, Mexico, and all through South America, wherever 

 there are active volcanoes. 



I will now give you the history of the volcanos of N. America. 



