216 ANNUAL OF SCIENTIFIC DISCOVERY. 



perfectly astonished at the force with which these gusts of heated air 

 rose vertically from the Val du Lys. Marked by the precipitated va- 

 pors which chanced to be afloat at the time, the vertical gusts were 

 often as violent as the draught from a factory chimney. Thus, given 

 the uplifted land, and we have a glacial epoch ; let the ice work down 

 the earth, every foot it sinks necessitates its own diminution ; the gla- 

 ciers shrink as the valleys deepen ; and finally we have a state of things 

 in which the ice has dwindled to limits which barely serve as a key to 

 the stupendous operations of a bygone geologic age. To account for 

 a glacial epoch, then, we need not resort to the hard hypothesis of a 

 change in the amount of solar emission, or of a change in the temper- 

 ature of space traversed by our system. Elevations of the land, which 

 would naturally accompany the gradual cooling of the earth, are quite 

 competent to account for such an epoch ; and the ice itself, in the ab- 

 sence of any other agency, would be competent to destroy the condi- 

 tions which gave it birth. 



STRUCTURAL ORIGIN OF ROCKS. 



It has long been known that pressure has an important effect on the 

 solubility of salts. Mr. Sorby, the well-known English geologist and 

 microscopist, has recently found, that by filling the tubes with which 

 he experiments, at a very low temperature, and placing them after- 

 wards in proper situations, he is enabled to keep the solutions which 

 they contain, under a pressure of from 2,000 to 3,000 pounds to the 

 square inch, for weeks or months continuously, and to watch the re- 

 sults. The pressure is measured and indicated by a capillary tube en- 

 closed within the principal one. The researches of Mr. Hopkins and 

 Prof. W. Thomson have made us acquainted with the effects of pres- 

 sure on fusion and freezing, and there appears to be an intimate connec- 

 tion between them and the experiments here under notice. Mr. Sorby 

 has proved that if a salt contract in dissolving it is more soluble under 

 pressure, and that if it expand it is less soluble. The law, as might be 

 anticipated, varies with the nature of the salt. For common salt it 

 may be stated thus : the extra quantity dissolved varies directly and 

 simply as the pressure. On comparing sulphate of copper with ferri- 

 cyanide of potassium under the same pressure, it is ibund that one 

 quantity dissolved of the former is ten times that of the latter ; and 

 there is a still greater variation of the mechanical equivalents. Rea- 

 soning upon the interesting facts brought out by this investigation, Mr. 

 Sorby concludes that the experiments " indicate that in some cases 

 pressure causes a slower and in others a quicker chemical action. And 

 I think it probable," he continues, "that further research will show that 

 pressure weakens or strengthens chemical affinity according as it acts 

 in opposition to or in favor of the change in volume, as though chemi- 

 cal action were directly convertible into mechanical force, or mechani- 

 cal force into chemical action, in definite equivalents, according to 

 well-defined general laws, without its being necessary that they should 

 be connected by means of heat or electricity." Apply these principles, 

 and it seems easy to explain peculiarities in the structure of metamorphic 

 rocks, to account for slaty cleavage, for some of the phenomena of 

 crystallization, that is, the direction in which the crystals are formed, 

 and for the impressions made by one limestone-pebble in another, as 



