80 Professor B. Silliman on Emerald Mckel 



In the analysis of recent corals, by Professor B. Silliman, 

 junior, published in the volume on Zoophytes by the writer, 

 there is less than one per cent, of magnesia. But in a com- 

 pact coral rock, made up of material of coral origin, he 

 found 38*07 per cent, of carbonate of magnesia. The coral 

 rock was a result of consolidation without heat, as we may 

 judge from the absence of all evidence of its effects. An- 

 other specimen of a fragmentary character afforded 5*29 per 

 cent, of magnesia. Both resemble the common reef-rocks. 

 They appear to shew that there are circumstances in which the 

 magnesian salt of the ocean, and the carbonate of lime of the 

 corals, may react and produce a magnesian rock at the ordi- 

 nary tropical temperature of water. This action pay favour 

 the consolidation into rock, which is in progress beneath the 

 sea-water. It is evident that the finer the coral or calcare- 

 ous material, the more magnesian the product. This prin- 

 ciple accounts for the small proportion of magnesia in the 

 second case alluded to above. — J. D. Dana.] — {American 

 Journal of Science and Arts, Second Series, vol. vi., p. 268.) 



On Emerald Nickel from Texas, Lancaster County, Pa. 

 By Professor B. Silliman Junior. 



This is the same mineral which I have before described 

 under the name of " hydrate of nickel."* The name now 

 proposed is in accordance with the custom of giving a trivial 

 name to mineralogical species, and has been suggested by 

 my friend Professor C. U. Shepard, as peculiarly appro- 

 priate, from the brilliant colour and transparency of the mi- 

 neral, resembling the emerald. The existence of carbonic 

 acid in this mineral as an essential constituent, was over- 

 looked by me, from the fact that it is all expelled at redness, 

 and was therefore in my analysis put down as water. The 

 water given off in the close tube does not change litmus 

 paper, and the mineral does not eifervesce in dilute cold hydro- 

 chloric acid. My attention was first directed to the probable 



♦ American Journal of Science and Art, Second Series, vol. iii., p. 407. 



