160 SEE— FURTHER RESEARCHES ON [April 24, 



water, often miles deep, resting on the ocean bed must tend to 

 force the fluid deeper and deeper into the bowels of the earth. A 

 study of what takes place on our earth under the observed con- 

 ditions constitutes therefore one of the grandest problems in nat- 

 ural philosophy. 



Indeed it may be said that the great laboratory of nature has 

 magnificent experiments constantly going on. All that we need to do 

 is to interpret these experiments correctly. The best way to do 

 this is to select phenomena in which the processes are so clear as to be 

 free from doubt; after we have found the law of the phenomena in 

 cases which are beyond question, we may then generalize and 

 interpret other phenomena, in which the relations are not so obvious. 

 By gathering principles and laws from cases which are entirely 

 clear, and working by degrees to understand those which are more 

 obscure, we may finally arrive at the true processes even when the 

 operations of nature are quite hidden from our view. 



Laws thus established by observation in the great laboratory of 

 nature will obviously hold true of like experiments in the minute 

 physical laboratories designed by man ; and by noting the phenomena 

 of the globe we may extend our knowledge of the universal proper- 

 ties of matter under various physical conditions often more extreme 

 than those ordinarily witnessed at the surface of the earth. 



§ 2. Heretofore the ocean bottoms have been assmncd to he zuater- 

 tigJit. — The earth's crust is made up chiefly of sedimentary, igneous 

 and granitic rocks, and soil produced by the decomposition of the 

 various kinds of rock under the action of water and the atmosphere. 

 Nearly all of the sedimentary rocks are quite leaky, and moreover 

 they absorb a great deal of moisture from the air; the formation of 

 artesian wells and of natural springs depends primarily upon the 

 percolation of water through rocks and layers of soil of various 

 kinds. The leaky character of the sedimentary rocks is well known 

 and has been generally recognized. But these rocks exist only 

 near the surface, and do not extend more than a very few miles 

 deep ; consequently they could admit the water to but a slight depth 

 into the earth's interior. Below the sedimentary rocks lies the 

 mass of granite which makes up by far the greater part of the 

 earth's crust. The granitic rocks, such as granite, andesite, dia- 



