OF PRE-CAMBRIAN ROCKS 211 
acter occur in the intervening tract of country. In the development 
of these rocks in the province of Quebec, however, the “Hastings” 
facies (see p. 201) is absent, the rocks being all highly altered, and 
resembling in this way those found in the Adirondack Mountains 
and in the more altered portion of the Ontario district. 
The “Original Laurentian area” and its easterly continuation 
above mentioned, like the area in eastern Ontario, occupy the southern 
portion of the Laurentian peneplain, underlying a great tract of 
slightly undulating country. They are composed of great bands of 
limestone interstratified with amphibolite and rusty weathering 
gneiss, often highly garnetiferous. This rusty weathering gneiss, 
where it occurs typically developed in the district about St. Jean de 
Matha, is found to be rich in sillimanite and to have the chemical 
composition of an ordinary clay slate. Bands of quartzite are also 
present in a number of localities, being interstratified with the 
gneisses and limestones above mentioned. Limestone, however, 
is the dominant rock of the sedimentary series. 
In Logan’s “ Original Laurentian area”’ this distinctly sedimentary 
series occurs in great folds, the horizons marked by the limestone 
bands, as mapped by Logan, striking across the country in a series 
of great sweeping curves. The large bodies of orthoclase gneiss 
which are present in the district and which Logan considered to 
form part of the sedimentary series, a more detailed examination in 
view of recent discoveries would probably show to belong to the lower 
igneous gneisses and to be of intrusive origin. 
Farther east, in the district to the north of the island of Montreal 
the lmestone series is not always so sharply folded, and in one 
portion of the district, over an area of about 750 square miles, it lies 
nearly flat, low quaquaversal dips being everywhere observed, the 
attitude of the beds suggesting that the whole series originally floated 
on a great body of the underlying granite gneiss. This farther 
north comes to the surface, the limestone series being torn to pieces 
by it, and the bathyliths thus emerging being traceable over great 
areas, the foliation of the gneiss presenting great sweeping curves 
to which the courses of the lakes and rivers in this northern country 
conform. It will, therefore, be seen that in all its features this devel- 
opment of these pre-Cambrian rocks in the province of Quebec 
