340 Herrick et al. on Ar.terican Norytes and Gabbros. 
most cases. Such rocks would be expected to resemble ordi- 
nary metamorphic sedimentaries in the inclusions. 
Garnet and the various metamorphic accessories then would 
be quite at home in the paragenous but foreign to the autogen- 
ous eruptives. Illustrations of these distinctions can be found 
in any highly metamorphic region, and while it ma}^ be easy to 
find instances where diory tes form apparently autogenous dykes, 
yet it is claimed that they may generally be traced to some re- 
lation with dykes of the first order and owe their origin to 
secondary fusion and perhaps also to a commingling of true 
igneous matter with such products of fusion as can be traced to 
the adjacent wall-rock. If this view be correct, the group at 
present under consideration may be regarded as standing on the 
boundary between the two classes. The resemblance between 
certain norytes, especially the olivine-bearing variety and dia- 
base, is so close as to baffle discrimination in the field. In like 
manner we shall be able to establish a close connection between 
gabbro and diabase in the Duluth locality. The present pur- 
pose is merely to call attention to three distinct phases of this 
group with some remarks upon the relations sustained by them 
to adjacent rocks, 
I. (1146) Olivine iioryte, near Marshall, N. C. (sp. gr. 
;:?.99.) This rock occurs about six miles northeast of Marshall 
{in the form of a dyke of variable width, penetrating the gneisses 
and micaceous schists, and forming the axis of a considerable 
area of metamorphism. The walls of the dyke are formed, in 
many places at least, by a zone of dioryte to be described fur- 
ther on. To the presence of this, or a related dyke, is jDrobably 
to be ascribed the segregation of ore in the iron mines in this 
locality. The tyi^ical phase of this noryte, as seen in the out- 
, crops at Bull creek, is a very coarsely crystalline purplish-black 
rock with well-defined black crystals of an orthorhombic min- 
rcral. The feldspar is in elongated narrow twins, while irregu- 
lilar, greenish, glassy masses of olivine can be distinguished here 
and there. The feldspar is very dark, evidently from a suffu- 
sion of the coloring matter of the bronzite. The only other 
ingredient which can be distinguished in the hand sample is 
nfiagnetite, to which the high specific gravity may be largely 
attributed. 
