Hydrate of Nickel, a New Mineral. 407 
mainly on the fact that no remains of fishes had ever been found 
in lower Silurian rocks, among the countless myriads of other ma~ 
rine animals, and that I was also influenced in my views by the 
proofs afforded by geological enquiry of a progression in creation, 
assiz has proved right in his conjecture that with such asso- 
ciates, fishes would sooner or later be detected. In one respect, 
indeed, I rejoice in the discovery, as the occurrence of an Onchus 
in upper Ludlow rocks and in Llandeilo flags, unites with other 
paleontological evidences to bind all the Silurian rocks together 
in one natural system. 
In conclusion, I would observe that whilst it is impossible, for 
the reasons above cited, to admit that the Silurian system can be 
broken into two systems, I might convince you, by another 
method of reasoning, that the adoption of such a proposition would 
entirely destroy the very term Silurian, in reference to regions of 
the continent of Europe, to which it has been applied, such as 
arge parts of Russia, Scandinavia, &c., where the lower Silurian 
alone is developed. But I have already said more than enough, 
and will only add, that notwithstanding our recent animated dis- 
cussions, Professor Sedgwick and myself have still as warm a 
friendship for each other as ever, and however he may ultimately 
_ persist in calling certain rocks of North Wales “Cambrian,” (al- 
though they are loaded with true lower Silurian fossils, ) I must 
seize this opportunity of declaring that I consider this to be little 
more than a geographical distinction ; and further, I must express 
my belief that if he should produce a work upon the geological 
structure of the old and slaty tracts of Britain, upon which he 
en long occupied, it will be found to be in every way 
worthy of his deservedly“ high reputation, and will throw impor- 
tant new lights on those parts of geological science which his elo- 
quence and memoirs have already adorned. 
Arr. XLIL—Hydrate of Nickel, a New Mineral ; by Prof. 
ae B. Si ie 
SiLuiman, Jr. 
Tas mineral occurs incrusting the surface of chromie iron 
from Texas, Lancaster County, Pennsylvania, and has been cir- 
culated among American mineralogists during the past year, un 
der the name of green oxyd of chrome. I found it, however, on 
analysis, to be a hydrous green oxyd of nickel nearly pure. "It is 
found in lustrous emerald green crusts, on the surface of some spe- 
cimens of the chrome iron from these mines; rarely in stalactites 
and columnar masses. It is often covered with a thin coating of 
carbonate of lime or magnesia which obscures its color. Alone it 
is quite transparent and of the most brilliant emerald green color. 
Hardness 3 or 3-25, being a little above cale spar. Gravity 3°0523, 
He 
