44 
An approximate determination of the relative abund- 
ance of these several rocks is afforded by an examination 
recently made by Professor Allan of specimens of 65 dykes 
occurring in various parts of Mount Royal and its vicinity 
and which may be taken as representative of the whole 
complex. His results show that the several types above 
mentioned were present in the following proportions :— 
Bostonite c3d.0.c0o 6 oe eee 4 
Ting waite: .eem.2k4 fies Oe 14 
Analeite:dy Kes: nec 806 eee 3 
Monchiguite <5. 08 dre ee 12 
Founchite ys.) ho00.c0.5 eee I 
Caniptonites ..c.si5 2.4 eee 30 
PAIN ONO igo 8 Se Sele Rs ee I 
65 
Bostonite.—Dykes of this rock are not very common. 
One of the largest was exposed in former years at 
the Reservoir Extension (see p. 49), representing the 
earliest of the several sets of dykes at this locality. It is 
of a buff colour and has the structure and appearance of 
a typical bostonite, but is a good deal altered. Dawsonite 
a remarkable carbonate of alumina and soda which was 
originally discovered at this locality occurs on the selvage 
of this dyke in contaet with the limestone. An analysis 
of the rock after treatment with nitric acid which removed 
3-33 per cent. of calcite, and smaller amounts of alumina 
and ferric oxide, is given under I on page 46. As will 
be noted, it has a high content of soda as compared with 
the potash. 
A bostonite sheet forms the greater part of Moffat’s 
Island, opposite Montreal. Dykes of the rock are also 
found in the tunnel which is being driven through Mount 
Royal. 
A small area of a reddish aplite cuts the camptonite 
breccia at Outremont. This is fresh and contains a little 
quartz. It is seen on the surface and is also traversed by 
the tunnel above mentioned. An analysis of the rock from 
the tunnel is given under IJ, page 46. It ranks as a 
phlegrose in the Quantitative Classification. 
Tinguaite.—This rock occurs abundantly in dykes 
and sheets, more especially in the district northeast of 
