138 NEW YORK STATE MUSEUM 
Syenite and Pegmatite 
The most interesting parts of this section so far as the struc- 
ture and origin of the vein and its contents are concerned are 
those lettered d and e, a combined specimen of which is shown 
in plate 1. This specimen shows the cellular and platy structure 
of the vein, the darker plates consisting of a pinkish brown manga- 
niferous calcite, and the lighter of crystalline quartz alternating with 
the darker bands and lining the cavities of the cells; but in the com- 
bined specimen the clear line of contract of the vein and footwall 
rock can be seen as well as the angular relationship of plates with 
the footwall. The microscopic study of the thin section taken from 
this contract shows that, instead of there being an almost knifelike 
line of demarkation between the vein and the footwall, there is an 
interfingering of manganiferous calcite plates with those of quartz, 
the former, where there is an angular relationship with the footwall, 
appears to be continuous with it but projecting inward with dove- 
tailed or interfingered plates of crystalline quartz projecting outward 
toward the footwall. We are led to believe from this observa- 
tion that the fractures filled now with the darker or carbonate 
material were filled by solutions flowing in part along the walls 
of the fissure and that the quartz filled fissures were afterwards 
filled by silica-bearing solutions coming or flowing from the inner 
parts of the vein. Positive evidence that the quartz is of later age 
than the carbonate is seen in many of the specimens where the 
quartz plates are found cutting and intersecting the carbonate 
bands at every conceivable angle and developing the box form 
which will be considered later on in this paper. 
Though the carbonate bands have apparently close connection 
with the wall rock indicated above, it is found that the wall rock 
d of the section given above is of a ferruginous nature, the red- 
dish pink coloration being due to hematite rather than mang- 
anese as is found to be the case with the carbonate plates. As 
the manganiferous calcite is more stable than carbonates con- 
taining iron, when they are found in the same solution, the fer- 
rous carbonate is deposited first and the manganese may be 
carried in solution much farther from the original source 
(Phillips, 4). It would seem therefore that the manganiferous 
plates could be a part of a ferruginous wall rock of calcite. 
Whether, on the one hand the fragments broken or sheared 
off from the Grenville marble were originally like the footwall 
or the fine-grained marble of the hanging wall and replaced by 
