179 



most important, (at least to the geologist,) acting through the 

 medium of heat, chemical combination, and crystallization. 

 The state of our knowledge of these, as a branch of physics, 

 is scanty and deficient, and was presented in the form of five 

 tables, shewing — 



1st. Bodies Jcnown to expand in volume by combination. 



2nd. Bodies known to expand in volume on changing 

 their state of aggregation or arrangement. 



ord. Bodies known to contract in volume in combination. 



4th. Bodies known to contract in volume in changing their 

 state of aggregation or arrangement. 



5th. Bodies whose volume is ^woz£;w to remain unchanged 

 in combination. 



After stating that these tables were only brought forward 

 as indicative of the class of forces proposed being treated 

 of, and pointing out some of the very singular facts which 

 they contain, of alteration of volume, and the immense force 

 with which it frequently takes place, the author proceeded 

 to apply the results of his own experimental determinations, 

 of change of volume, in solutions of chloride of calcium 

 and sulphate of soda, on mutual decomposition, and of the in- 

 termediate oxide of iron in passing to peroxide — to the salt 

 formation of England — and shewing, that if considered as a 

 chemical deposit, an elevation of the surface, of eight feet 

 six inches, will have been produced, by reason of this change 

 of volume only. 



A case of observed expansion in volume, by further 

 oxidation of the blue marl, of the saliferous system, and 

 its remarkable effects, was brought forward, and analogy 

 shewn with the indurating marl forming the bottom of Lake 

 Superior. The effects of these sweUings, in all directions 

 of a mass, in producing consolidation and integration of its 

 parts, is there pointed out. 



The author then proceeds to apply this principle, to ac- 

 count for the formation of the contemporaneous quartz veins 



