194 J. S. Hunt on the Crystalline Limestones of N. America. 
repose horizontally upon the disturbed strata of this oldest Ameri- 
cau system, a southern prolongation of which crosses the Otaway 
near Bytown, and the St. Lawrence at the Thousand Isles, and 
spreading out, forms the mountainous region of northern New 
Yor “his series consists in large part of a gneiss, which is 
often garnetiferous; but beds of mica slate, quartz and garnet 
rock, hornblende slate and hornblendic gneiss are also met with, 
besides large masses of a coarsely crystalline, often porphyritic 
rock, consisting chiefly of a lime and soda feldspar, which is 
sometimes labradorite, and at others andesine, or some related 
species, and is generally associated with hypersthene, It often 
holds beds or masses of titaniferous iron ore, and from its extent, 
occtipies a conspicuous place in the series. It is the hypersthene 
rock of McCulloch and Emmons. 
With these, the limestones are interstratified, but their relations 
to the formation have not yet been fully made ont. f th 
rocks bear evidences in their structure, that they are of sediment- 
ary origin, and are really stratified deposits, but their investiga 
tion is rendered difficult by the greatly disturbed state of the 
whole formation. Among these stratified rocks, there are how- 
ever dykes, veins, and masses of trap, granite and syenite, often 
of considerable extent, which are undoubtedly intrusive. ‘There 
are abundant evidences that the agencies which have given to 
the strata, their present crystalline condition, have been such as 
to reuder the limestone almost liquid, and to subject it at the 
same time to great pressure, so that in many cases it has flowe 
around and among the broken and often distorted fragments of 
the accompanying silicious strata, as if it had been an inject 
hypogene roc 
The limestone strata are from two or three feet to several hun- 
dred feet in thickness, and often present a succession of thin beds, 
divided by feldspathic or silicions layers, the latter being somes 
times a conglomerate of quartz pebbles and silicious sand ; in oue 
instance, similar pebbles are contained in a base of dolomite. 
Beds frequently occur in which the carbonate of lime 
J 
pure state, bnt in other cases they are intermixed with quart, 
carbonate of lime, orthoclase, scapolite, sphene and other specles 
finely granular or almost compact; their color is white Ing 
into reddish, bluish, and grayish tints, which are often arranged 
in bands coincident with the stratification. Some of the dark 
grey bands, harder than the adjacent white limestone, were found 
by Mr. Murray to owe their color to very finely dissem! 
