and the allied Rocks. 57 



the circumstances attending submarine igneous action, I am 

 persuaded, are not generally apprehended. What is the con- 

 dition of the deep bed of an ocean ? Even at a depth of 

 three miles, the waters press upon the bottom with a force 

 equivalent to a million of pounds to the square foot ; and with 

 such a forcing power above, can we set limits to the depth to 

 which these sea-waters — magnesia and soda solutions — will 

 penetrate ? Will not every cayern, every pore, far down, be 

 filled under such an enormous pressure ? Let a fissure open 

 by an earthquake effort, and cau we conceive of the tremen- 

 dous violence with which the ocean will rush into the opened 

 fissure ? Let lava ascend, can we have an adequate idea of 

 the effect of this conflict of fire and water? The rock rises, 

 blown up with cavities like amygdaloid, and will a long in- 

 terval elapse before every air-cell will be occupied from the 

 incumbent water ? Suppose an Hawaii to be situated beneath 

 the waves, pouring forth its torrents of liquid rock ; — this 

 island contains about five thousand square miles, which is less 

 than the probable extent of many a region of submarine erup- 

 tion ; — suppose, I say, the fires were opened and active over 

 an area of some thousands of square miles — are there no 

 effects to be discovered of this action ? There is no geologist 

 that pretends to deny the premises — the fact of such submarine 

 eruptions, the ocean's pressure, the effect of fire in heating 

 water, and in giving it increased solvent power ; and why 

 should they not reason upon the admitted facts, and study out 

 the necessary consequences ? Surely, if there have been effects, 

 we might expect to see some of them manifested in the cavi- 

 ties oi the ejected rocks, which were opened at the time to 

 receive the waters and any depositions they might be fitted 

 under the circumstances to make. 



We are led by these considerations to another point in con- 

 nexion with this subject, — the probable condition under which 

 the different amygdaloidal minerals have been formed. Have 

 they all proceeded from heated solutions, or all from cold so- 

 lutions ? or can we distinguish some which are indubitably of 

 one or the other mode of formation ? 



Bearing on these questions, we notice such facts as are af- 

 forded by the condition and relative positions of the minerals 

 in geodes. And I would here acknowledge my obligations to 

 the valuable memoir, before alluded to, by Messrs. Jackson 

 and Alger. The paucity of information on this subject to be 

 found in the various accounts of similar rocks by other writers 

 is surprising. Even where special pains have been taken to 

 describe the mineral species, the relative positions of the mi- 

 nerals are very seldom noted. It^has been altogether too com- 



