294 J^f^c /\))icrican Geologist. November, 1900 
This theory would explain very well the corrosion which 
the older elements of the rock have suffered, notably the feld- 
spar and the apatite; it would explain the modifications which 
the pyroxene has suffered; but the same difficulty presents 
itself as in the preceding case ; and, moreover, if such exomor- 
phic phenomena are common in fragmentary rocks enclosed 
within volcanic rocks, it is still difficult to understand how 
they could exist in such constancy throughout so large a 
mass. 
3. The last hypothesis, and the one explaining best all 
the phenomena, consists in supposing that the orthoclase is 
an original element of the magma and crystallized directly 
from the latter. 
The corrosion of the other minerals of the rock which it 
has caused is then of the order of that which is often seen in 
the phenocrysts of the volcanic rocks when they have a com- 
position dilifering from that of the analogous minerals, of the 
second consolidation, and of the order of that so often seen m 
the zonal plagioclases of the endomorphosed deep-seated 
rocks, etc. 
As for the cause of the differences of composition between 
this orthoclase gabbro and the other gabbro types described in 
this paper; a careful study of the local field geology will per- 
haps enable one to see if it does not bear a relation to the po- 
sition of this rock at one of the extremities of the gabbro re- 
gion, and to determine if it is not connected with the nature of 
the older rocks in contact with which the orthoclase gabbro 
finally solidified. 
Chapter VII. Cordierite Noryte. 
The term noryte was proposed by Esmark* in 1838 to 
designate certain rocks of widespread occurrence in Norway, 
consisting essentially of plagioclase and hornblende, with or 
without accessory diallage, or hypersthene. In current usage, 
liowever, noryte signifies a holocrystalline granitoid rock con- 
sisting essentially of a plagioclase feldspar and a rhombic 
pyroxene; and it is in this sense that the word is used in this 
article. A typical noryte, therefore, differs from a normal 
*Esmark: Magas. f. Naturvid. 1838, I. p. 207 Ref. Zirkel: Petrog. 
1894. n. pp. 785- 
