194 Notes Illustrative of the 



primary formations of these segregations of simple minerals 

 in the rocks of which they form constituent parts, is a 

 most interesting, but as yet unsolved question, and one 

 attended with peculiar difficulties when experimentally in- 

 vestigated, from the circumstance that the phenomena in 

 question require periods of such extent for their deve- 

 lopment, as to make it impossible to institute in the la- 

 boratory any experiments which would be strictly, and 

 in all points analogous to what obtains in nature. In their 

 original state of igneous fluidity, the operation of the at- 

 tractive affinities of the molecules of which the different 

 minerals forming granitic rocks are composed would be 

 free and uninterrupted, as has been satisfactorily shewn by 

 the " pyrochemical" experiments of Maesterlich, and others, 

 who have succeeded in obtaining crystals of the minerals 

 alluded to, from the igneous fusion of their constituents. 

 But, the obtaining of these in their crystalline state, only 

 as detached and individual substances, leaves us still in 

 doubt as to the causes of some of them occurring massive 

 and disseminated. Thus among the others, a curious and 

 most interesting fact stated by Mr. Babbage in his " Econo- 

 my of Machinery," appears to warrant the conclusion, that 

 such segregations take place when the substances are in 

 a state of aqueous fluidity ; for he remarks, " Flints after 

 being burned and ground are suspended in water in order 

 to mix them intimately with clay, which is also suspended 

 in the same fluid for the formation of porcelain. The 

 water is then in part evaporated by heat, and the plastic 

 compound out of which our most beautiful porcelain is 

 made remains. It is a curious fact, and one which requires 

 farther examination than it has received, that if this mix- 

 ture be suffered to remain long at rest, before it is worked 

 up, it becomes useless : for it is then found, that the silex, 

 which at first was uniformly mixed, becomes aggregated 

 together in small lumps. " This parallel," he adds, " to 

 the formation of flint in the chalk strata deserves atten- 



