156 Bigsby— On the Laurentian Formation. 
the syenitic or hornblendic; thereby simply expressing what is 
continually taking place, the preponderance of one or other. The 
second form is very prevalent. ‘The beds accompanying Laurentian 
gneiss in the Canadas are crystalline limestone, anorthosite, quartzite, 
hornblende-rock, granite, and micaceous, hornblendic, and chloritic 
slates, relatively abundant in the order they are here set down ; the 
hornblendic slate is more abundant near marble, and the chloritic 
slate is in much smaller masses than in the succeeding Huronian 
formation. The quartzite occasionally interleaved with this gneiss 
may vary; but it is usually white, translucent, granular, and seldom 
conglomeratic. 
2. The Crystalline Limestone.—This is either pure white or grey, 
and often has broad grey bars owing to finely diffused graphite. The 
phosphates which it holds in great abundance will be spoken of in 
the sequel. Its crystallization is always coarse, and sometimes ex- 
tremely so; single crystals being sometimes two or three inches wide. 
It is seldom saccharoid, and almost everywhere alternates with 
gneiss, in bands from 50 to 1,500 feet thick, as I have seen it near 
Gananoque, on the Lake of the Thousand Isles, and on the Mattawa, 
an affluent of the Upper Ottawa River, and elsewhere. ‘The Nor- 
wegian representative of this marble is in much less quantity. The 
bands of this Canadian marble are tortuous, and often, by bending 
round sharply, they return by a parallel course to within a short 
distance from their visible point of departure. Corrugated seams 
of gneiss are sometimes inclosed in the limestone. 
In the township of Bastard, on the River Ottawa, and of Madoc, 
on Lake Ontario, the Geological Commission met with two forms of 
conglomerates and grits, which are decisive of the sedimentary origin 
of the Laurentian beds of Canada, and therefore of the highest in- 
terest.* As an instance, in Bastard township there lies between two 
beds of white marble a fine-grained quartzose sandstone, with pebbles 
of grey calcareous sandstone, phosphatic, with others of vitreous and 
opalescent quartz; the mass of sandstone being at the same time in- 
terspersed with mica and graphite; the dip is ENE.z 30°. We 
have another example of this near Madoe Village, where, resting on 
marble bands, are two other conglomerates, totally different. One 
is a bluish micaceous schist, holding numerous fragments of green- 
stone and syenite: the other is a dolomite with large pebbles of 
quartz, felspar, and a few of calespar. 
3. The Lime-felspars, or Anorthosite.—In the latter part of the 
‘Report for 1863’ it is intimated that the anorthosite constitutes a 
separate, newer, and unconformable formation. The discovery in many 
parts of Canada of lime-felspar-rocks in large tracts is wholly due 
to the Government-Survey of the Colony. It is of much importance, 
both geologically and economically, as it explains the unexpected 
fertility of an extensive district to the north of Montreal, which had 
been previously supposed to be gneissic and comparatively barren. 
On the Lower Ottawa this lime-felspar-rock is 10,000 feet thick, 
* In 1846 Elie de Beaumont announced the sedimentary nature of the Swedish 
sneiss ; Bullet. Soc. Géol. France, n.s. vol. iv. p. 501, . 
