GEOLOGY. 207 



established. It is probable that this cooling is, however, to a great 

 extent effected by the innumerable currents of water and gases 

 which circulate in every direction through the interior of the globe, 

 and of which volcanic eruptions, hot springs, and suffioni are only 

 the more violent manifestations attaining the earth's surface. The 

 recent ingenious experiment of Daubree has shown us that water may 

 be drawn by capillary force towards spaces heated much above its 

 boiling point. The water thus conveyed, in passing into the state of 

 vapor, does not everywhere produce volcanic phenomena, for these 

 probably require the concurrence of conditions which are not often 

 found. The aqueous vapor will ordinarily ascend to colder portions 

 of the earth's crust, and ther, yielding its heat to the walls of the fis- 

 sures, will flow back in the liquid state to the source of heat to repeat 

 the same process, while on the other hand currents of cold water will 

 absorb the heat thus conveyed to the rocks and bring it to the sur- 

 face by thermal springs. 



The general permeability of rocks is so well admitted by most geol- 

 ogists that I have not thought it necessary to seek for proof of it in 

 the discussions of the present question ; the brilliant conception of the 

 nietamorphism of rocks by the humid way, which has been so well 

 maintained by the ablest chemists, is only possible on this condition. 

 The permeability of rocks also explains in a satisfactory manner the 

 formation of agates, and of zeolites, arragonite, and other minerals in 

 the midst of the most compact basalts, and of geodes of quartz, in the 

 Norwegian granites. We may also recall the artificial colors whk-h 

 are given to agates. Mr. Damour has even shown by a series of 

 curious experiments that the water which is ordinarily considered as 

 chemically combined in certain hydrated silicates, such as zeolites, 

 may be in part extracted from them, and again restored, without 

 any apparent alteration in these minerals. 



peptli of the Ocean. In the above article, Mr. Saemann has quoted 

 Laplace's inference of GOO meters (near 2000 feet) for the mean depth of the ocean. 

 All researches tend to show that this depth is very greatly less than the actual 

 depth ; the data on which Laplace's conclusion was based are also quite conjec- 

 tural. The area of laud to sea is now stated as 3 : 8, and not, as formerly, 1 : 3. 

 This would render the ocean even shallower than was stated by Laplace; while 

 every modern observation in deep soundings, and above all the discussion of 

 waves of translation in earthquakes, proves it vastly deeper. 



The discussion of the Japan earthquake wave in 1854 by Prof. Bache, gave for 

 the depth of the Pacific Ocean in the path of the 8ii^)da waves to San Dictro and 

 San Francisco (34 40/, 32 42', 37 480 a depth of 2,2ff to 2,100 fathoms (13^380 to 

 12,000 feet). 



Young estimates the average depth of the Atlantic at about 15,000 feet, and of 

 the Pacific about 20,000 feet. 



Guyot derives from the law of the relief of continents about 15,000 feet for the 

 South Atlantic, which he suggests may be too little. 



Herschcl derives from the velocity of the tide wave, according to Airy's table, 

 22,000 feet for the Atlantic basin from lat. 50 S. to lat. 50 N. He thinks that an 

 average depth of four miles is rather above than below the true depth. 



Kloden assumes a probable average of three and a half miles, or about 18,000 

 feet. 



There is certainly a wide difference of statement among these authorities, but 

 we seem authorized in assuming a mean depth for the great oceanic basins of 

 15,000 to 18,000 feet. The greater of these numbers would still leave Mr. Srcmann's 

 conclusions on the absorbability of the waters of the globe by its rocky mass 

 quite within the range of probability. Silliman's Journal. 



