308 B. K. Emerson—Dyke of Elwolite-syenite in New Jersey. 
the elxolite (ce) which has taken its shape entirely from the 
receding minerals and which thus closed the series. 
Out on the plateau of metamorphic rock I picked up a curi- 
ous mass not in place, which showed a contact of foyaite on 
foyaite of different age. The older was coarser grained than I 
found it elsewhere and richer in orthoclase, being largely made 
up of crystals 25-30"™ long, distributed porphyritically in a 
fine-grained rusty ground containing pyrite. The newer rock, 
resting on this, has a rudely columnar structure at right angles 
- to the plane of contact, resembling somewhat the gypsum crusts 
from salt vats. 
The columns of which this layer consists are elongate imper- 
fect crystals of orthoclase and eleolite and bundles slightly 
radiated of a greenish black hornblendic mineral. Small tufts 
and spheres of the latter are also scattered through the mass, 
together with some dark purple fluor and much pyrite. 
Under the microscope distinct crystals of elzolite appeared 
and the hornblende needles were contracted, like the handle 
that the hornblende ha ere commenced its crystallization 
first and that the two minerals had thereafter increased to- 
geth 
a plum twig. Only rarely in unchanged non-fibrous portions 
_ Decomposition has everywhere affected the superficial por- 
tions of the dyke, and at the summit where the rock is coarsest, 
extended quite deeply, but without the formation of any zeolitic 
minerals, 
Amherst College, Massachusetts, April, 1882, 
