232 Scientific Intelligence. 



With reference to the handed or endogenous type of agates the 

 authors remark: 



"Assuming hypothetic-ally a rock ca\ it v containing a solution of 



meated with an acid solution or gas, we should naturally expect to 

 tin.! a layer of silica deposited on the walls of such a cavity, and, as 

 the action continued, more and more silica would be deposited; 

 and if the solution were enclosed in the rock cavity, the central 

 portion would, when the action had continued to a certain point, 

 set in an amorphous mass. This action is very completely paral- 

 leled in some of the preparations which we have made, and in 

 some of these we have found that a central vacant space was left, 

 owing to there not beimr enough silica in the solution to till the 

 whole cavity when precipitated in the gelatinous form. This is 



By t 



pletely reproduced. When the precipitated silica in these pre 

 rations is exposed to the air it, for the most part, dries up ; 

 crumbles away, although some forms closely like common opal 

 appearance but of lower specific gravity have been produc 



think that the natural agates and allied varieties might be imitat 

 not only as here inform but also in hardness and stabilitv. — b 

 J/<>7.. Mav, 1882. 



6. The Origh, and delations of the Carbon minerals, 

 Professor J. S. Newberry. 24 pp. 8vo. From the Annah 

 the N. Y. Acad. Sci., vol. ii, 1882.— Professor Newberry, on 



tion as to the origin of the mineral oil, and opposes the v 



that it is indigenous in the sand-rocks which hold it, expressed 



he <l|l»|t .'t, I },e ehclni.it r\ , t he ■. 



•and of pangenesis o! minerals, t he classt- 



r ;»er<rfs. — Professor L. [. [oki.stuom has re- 

 ew inin.-rals from Wermland, Sweden. Man- 



