Geology. 283 
iron, Some of these rocks pass into phonolites throngh the admixture 
of asilicate which gelatinizes with acids and has the composition of 
natrolite, This mineral in one case amounted to more than 400 p. c. 
. the rock, the remainder being orthoclase with a small amount of car- 
nates, 
Dolerites are also abundant, and sometimes pass, owing to a scarcity 
of ( dspar, into an augite rock, generally with ilmenite and magnetite. 
a) — 
_, ladorite, with sparsely disseminated crystals of black augite, a little 
brow mica, and a great abundance of crystals of honey-yellow olivine, 
hich amount to more than 45:0 p.c. of the mass. e composition of 
this olivine I have found to be silica 37°17 , Magnesia 39°68, protoxyd of 
99°39 
the intrusive rocks 
Parts of Scandinavia, and the subjacent gneiss.—(Bul. Soe. 
i, 33 
granitoid trachytes as well as the dolerites, diorites and peridotite 
ck) make up mountain masses, while the earthy and _por- 
ytes and the phonolites are generally found cutting the 
sl, and the adjacent strata. The absence of quartz or of any excess 
;@ from all these rocks is a remarkable feature. Farther to the 
: hen intrusive granites are very abundant; these penetrate the 
: wu strata but are older than the carboni 
4. Pocks are also abundant in the county of Grenville, where they 
Martz, e 
' of orthoclase with’ an excess of silica and a little oxyd of iron. 
i are cut by large veins of chert, and in the vicinity of these 
0 changed j caoli iti 
P of igneous rocks, which is overlaid by the Potsdam sand- 
Very unlike those which we find penetrating the paleozoic 
