On Solutions of' S ilex in the Cavities of' Minerals. 141 



strange mistake, he calls them microscopic fluids, and as dis* 

 cernible only by the aid of powerful microscopes. If the author 

 had read with care the account of these fluids, he would have 

 found that some of the cavities (the one in Mr. Allan's fine 

 specimen, for example) are nearly the Jfth of an inch long, 

 and that the fluids have been taken out of the cavities, looked 

 at with the naked eye, and touched, tasted, and subjected to 

 chemical experiments. Having corrected this misapprehen- 

 sion, arising no doubt from the author's quoting from me- 

 mory, we proceed to the facts themselves. 



" When Mr. B. F. Northrop, of Yale College, was breaking some ballast 

 stones, from New Orleans, consisting of hornstone, flint, chalcedony, 

 and quartz pebbles, he found many of them with cavities lined with crys- 

 tals of hyaline quartz. Some of the cavities were lined with mammil- 

 lary chalcedony, and others with a white spongy deposite resembling an 

 earthy precipitate. Upon breaking an oval pebble of hornstone, whose 

 diameter was three inches by two, Mr. Northrop found in its centre a 

 cavity of three- fourths of an inch by half an inch, filled with a milky 

 fluid, like water containing magnesia. 



He unfortunately spilled the greater part of the fluid, and before the 

 remainder could be secured, it was exhaled (it being a very hot day) 

 by a rapid evaporation, leaving a white spongy precipitate lining the ca- 

 vity, and staining the surfaces of fracture. During this rapid evapora- 

 tion minute prismatic crystals shot from the Jluid, even under the eye of 

 the observer, occupying not only parts of the cavity, but also of the sur- 

 faces of the fracture. Both the crystals and the spongy mass were easily 

 ascertained to be silex. They neither effervesced nor dissolved in acids, 

 and when rubbed between surfaces of glass, they took hold of it with 

 great eagerness, instantly depriving it of its polish, and scratching it as 

 distinctly as a file does iron. 



This was true, not only of the spongy matter, but of the separate crys- 

 tals, which we are entitled to consider as crystals of quartz, almost in- 

 stantaneously deposited, from a rich silicious solution. These crystals 

 were of a rather dull white, without much lustre or transparency. Their 

 diameter was that of fine sewing silk, and their length not exceeding 

 one-sixth of an inch. It is much to be regretted, that no' opportunity 

 was afforded of examining the fluid, so that it is impossible to say whe- 

 ther it was some modification of water, or a distinct fluid. The earthy 

 deposite, and the crystals were tasteless, and proved to be a very sharp 

 grit between the teeth. 



In the centre of another pebble, five inches by three, and consisting of 

 a mixture of hornstone and chalcedony, Mr. Northrop found another 

 cavity of one and a half by one inch, nearly filled with the spongy sili- 

 cious deposite already described, hut it was still moist, to such a degree, 



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