‘\ 
57 
Many of both adjacent rocks are found in-an altered 
state imbedded in the trap; which, with the filtering of the 
limestone, prove the deposition a true dyke. 
The mass of the rock consists of greenstone, sp. gravity 
2.87, of a dark green, but frequently veined and mixed with 
many other minerals. 
In the centre of the exposed portion of the dyke rises a 
large vein of nearly white hornstone, presenting very inte- 
resting characters. It contains no imbedded minerals, and 
is homogeneous in structure, but with a lamellar or pseudo- 
crystalline arrangement. Its planes are vertical, and at its 
junction with the trap it is moulded to it, but not adherent, 
and appears to have been formed from rocks at a greater 
depth than the trap, and ejected through it. The minerals 
found imbedded in this trap rock are various; specimens 
have been obtained of mica, chlorite, felspar, albite, olivine, 
augite, amphibole, epidote, apatite, adularia, chalcedony, sul- 
phate oflime, probably anhydrite, baryto-calcite, arragonite, 
calcareous spar, fluor spar, galena, iron pyrites, sometimes 
magnetic. Epidote is found also on Mutton Island. 
The general mass of this trap rock possesses a hidden 
nodular structure, only developable by blasting. The no- 
dules consist of precisely the same material as their matrix, 
and having the same cohesion, they cannot be detached 
by the, hammer. 
The nodules are from eighteen inches in diameter to the 
size of a nut; they are sometimes found pressed together in 
masses with flat sides, like bubbles. Crystals occurring at 
the surface of a nodule do not pass into the matrix, but are 
truncated thereby. In some cases the nodular structure is 
gradually obliterated, and the usual homogeneous one re- 
places it. 
This nodular formation is essentially different from any 
hitherto described,—as the orbicular granite of Corsica and 
South of France, the. onion stone of the causeway, &c., 
