Formation of Qudtrtz Crystals ^^c, from Siliceous Sohitions. 29 



similar facts, and even with facts far more puzzling than those of 

 M. Repetti. Our mineralogists and geologists and natural phi- 

 losophers never doubted the testimony upon which these were 

 published ; and, with the exception of some red-hot Plutonists, 

 whose prejudices were opposed to the belief that many minerals 

 have been, and are now, forming from aqueous deposition, we 

 never met with any unprejudiced philosopher who did not ad- 

 mit the facts as implicitly as any other in physical science. For 

 our part, we cannot see where the wonder lies. Among the 

 extraordinary facts on which every science is founded, and many 

 of which are every hour obvious to our senses, is it at all a mat- 

 ter of wonder, or is it even slightly marvellous, that a soft 

 transparent siliceous mass should be found in the cavity of a 

 calcareous rock, and should harden into something like calce- 

 dony or porcelain, or that a calcareo-siliceous gelatinous mass 

 should become solid, opaque, and friable? 



The following are a few of the facts which ai'e impressed on 

 our memory, and which it may be interesting to bring to- 

 gether. 



1. Spongy Amorphous mass of Carbonate of Lime formed 

 by the evaporation of a Fluid in a Cavity. — Count Bournon, 

 Mineralogy, vol. ii. p. 35, informs us, that in the vicinity of 

 Lyons there is a calcareous rock containing often very large 

 geodes, having for their envelope silex mixed with lime, fre- 

 quently alternating in concentric layers. Within these geodes 

 beautiful crystals of carbonate of lime occur, mixed with those 

 of quartz, which they rivalled both in transparency and per- 

 fection of form. Upon breaking numbers of these geodes, 

 Count Bournon found some of them full of water, and on one 

 occasion he obtained half of a geode with the water which it 

 contained unspilt. Observing that the fluid moved with a 

 massy heaviness like mercury, he concluded that it must be a 

 very concentrated solution ; and as this happened at mid-day 

 in a warm day in July, the fluid was all evaporated in little 

 more than a quarter of an hour, and there reinained in the 

 geode a spongy amorphous crystalline mass of carbonate of 

 lime. 



About the same period Count Bournon observed the same 



