'jidS The American Geologist. December, itm 
surface and is an extreme for an eruptive mass. Finall}'. the 
diabase lies on the surface of a surface flow, hence it must be a 
surface flow itself. 
Compression has produced little change in the quartz-porphyry 
except the distortion of folding. Along two faults at the east 
base of South mountain and east of FroHt Royal, the quartz- 
porphyry has been dragged out into a lustrous mica slate of very 
fine texture. In some places there has also l)een produced a small 
amount of schistosity. As a rule it has suffered no change when 
compared with the diabase, a ditlerence to l)e attributed to its 
simpler chemical composition (nearly pure silica) and to its greater 
mechanical strength. 
The diabase has uniformly received a strong schistosity and 
rearrangement of minerals. Muscovite, biotite, chlorite, epidote, 
and (juartz have been developed everywhere; and locally amygdu- 
loids occur with jasper, quartz and epidote. The epidote and 
quartz occur lioth in disseminated grains and in lenses attaining a 
thickness of four feet. Cases of unaltered dinhasc are very rare, 
but occasionally occur. 
In addition to these igneous rocks, a considerable number of 
small dikes belonging to the Jura-Trias system were seen. These 
occur throughout the mountain region, but are most frequent in 
the granite tract. 
To sum up, the sequence of the rocks in the mountain region is 
as follows: 
Siluro-Cambrian Limestone. 
Cambrian Sandstone. 
Shale. 
" Sandstone. 
Slate. 
. . CTranite. 
Diabase. 
Quartz-porphyry. 
Their physical history is, in brief: 
Surface flow of quartz-porpliyry followed after short interval 
by surface flow of diabase. Injection of granite into the 
diabase, presumably passing through the quartz-porphyry. 
Dynamic action and production of schistosity in diabase. . .Erosion. 
Submergence and deposition of Palaeozoic strata. Dynamic 
action with folding, cleavage, and elevation Erosion. 
Submergence and .Tura-Trias deposition. 
