428 
Geology* 
which took place within the primitive period, and must 
therefore be considered as a later production than rutile. 
Here a consideration of the laws of crystallization coun- 
tenances the observations on the order in which primitive 
rocks follow one another. The rutile, consisting of few 
and simple elements, of cotemporary origin with a gra- 
nite, in which rock-crystal occupies the place of quartz, 
and adularia that of common felspar, sufficiently 'be-, 
speaks a period, when the solution, being purer and more 
tranquil, furnished an earlier and purer crop of crystals ; 
while the confused and irregular crystallization of primi- 
tive trap and sienite, together with the greater impurity of 
the felspar, and very compounded nature of the horn- 
blende and rutilite, indicate an inferior purity of the solu- 
tion, and consequently later precipitation of the crystal- 
lized mass,” 
d. JYigrine *—' This species has been hitherto found only 
at Ohlapian in Transylvania, in alluvial hills, consisting 
of yellow sand, intermixed with fragments and boulders 
of granite, gneiss, and mica- slate, and from which gold is 
obtained by washing. This gold is the purest found in 
Transylvania ; a circumstance sufficiently indicating, that 
it belongs to a different, and consequently earlier forma- 
tion, than the usual Transylvanian native gold, which oc- 
curs there in clay- porphyry, grey-wacke, and grey-wacke 
slate, and belongs to the brass- yellow variety, from the 
considerable alloy of silver which it contains. In these 
stream-works, the nigrine is obtained at the same time 
with the gold, and comes to us intermixed with grains 
of rutile, precious garnet, kyanite, and common sand ; 
which renders it extremely probable, as Dr. Mitchd re- 
marks, that this fossil, also, is a native of primitive moun- 
tains.* 
* Vide Mitchell, in Irish Transactions, 
