GEOLOGICAL NOTES IN THE GEEA.T EXHIEITION-. 
389 
The proximity of the serpentine leaves no doubt as to their geolo,£yical 
horizon being that of the Quebec group of the Lower Silurian. Four 
other samples of slates have been sent to the Exhibition ; of these, the 
Cleveland and the Shipton slates are a continuation of the Melbourne 
band ; the slates from Orford may be of the same band ; but the geological 
horizon of those from Tring is uncertain, although they probably belong to 
the Quebec group. The Kingsey slates appear to be lower in the series 
than the magnesian group of strata. Flagstones are exhibited from the 
Medina " grey band," and hydraulic lime from the Clinton formation at 
St. Catherine's. The bed which yields this — "the Thorold cement" — is 
a dark brown dolomite, and 80,000 bushels have been annually made. 
There is another sample of hydraulic lime from Walkerton, made from 
beds of 2 to 11 miles, occasionally separated by layers of shale, in the 
total amounting to 15 feet, and belonging to the Onondaga formation. 
The practical manufacture of this latter cement has not however been yet 
attempted for commercial purposes. Other samples are also samples 
from Limehouse (Clinton group), Nepean (Chazy formation), Rockwood 
(Niagara group), and Magdalen E-iver (Hudson Eiver formation). Com- 
mon lime is shown from stone belonging to the Guelph and Onondaga 
formations, and from the building-stone of Montreal, where 270,000 tons 
are annually made. 
The common bricks exhibited are all made from drift or alluvial clays. 
Whetstones are shown from the Quebec group, Hudson Eiver, and Medina 
formations. The mica-slates also which are associated with the crystalline 
limestone of the Laurentian series are frequently of the character required 
for scythe-stones. The whetstone rock occurs in immediate contact with 
a thick band of conglomerate, the pebbles of w-hich are frequently large, 
some of them 6 inches in diameter ; they are chiefly of quartz, but some 
are of feldspar an^ some calcareous. The quartz pebbles are for the most 
part distinctly rounded. Some of the siliceous slates of the Huronian 
series yield very fine hones ; they are usually of a green colour, and 
occupy a place in the lower part of the series. Grindstones are shown 
from the Medina " grey band," and millstones from the Oriskany forma- 
tion. Millstones or dressed buhrstone (Laurentian) is also exhibited from 
Grenville. This buhrstone constitutes a series of veins cutting an intru- 
siA^e mass of syenite, which occupies an area of 36 square miles, amongst 
the Laurentian rocks of Grenville, Chatham, and Wentworth. The veins 
consist of yellowish-brown or flesh-red cellular chert, and the stone ]:as 
the chemical composition of flint or chalcedony. The attitude and asso- 
ciations of the chert show clearly that it cannot be of sedimentary origin, 
and its composition taken in conjunction with the igneous character of the 
district suggests the idea that it is an aqueous deposit which has filled up 
fissures in the syenite, and is similar in its origin to the agate or chalce- 
dony which in smaller masses are common in various rocks. For a distance 
of perhaps 200 yards on each side of these veins of chert, while the quartz 
of the syenite remains unchanged, the feldspar has been more or less 
decomposed, and is converted into a sort of kaolin. As this process 
involves a separation of the silica from the feldspar, it is not improbable 
that it has been the origin of the veins of silex. 
Mineral manures are now an important division of economic geology. 
Gypsum is shown from the Onondaga formation on the Grand Eiver; al- 
luvial freshwater shell-marl from deposits at New Edinburgh, Montreal, 
and many other places ; and calcareous marl is shown from Noisy Eiver 
falls, where it covers the extensive slopes on both sides of the river, pro- 
bably covering an area of 300 acres in the vicinity of the falls, with an 
