762 REVIEWS 
of quartz were clearly formed before the magma rose to the surface and 
their corroded or embayed condition is due to resorption by the magma. It 
is generally assumed that the relief of pressure causes a change in equi- 
librium and as a result of relief the magma ceases to precipitate quartz and 
dissolves some of that which has been precipitated. Does the presence 
of quartz instead of tridymite show that the temperature of solidification 
was less than 800°? In the case of granitic rocks where the last crystals 
formed are an eutectic, the temperatures there are low, but in the porphyries 
containing resorbed quartz the latter must have been present in excess of 
the eutectic for the temperature and pressure prevailing at the time. 
If the pressures do not seriously affect the quartz thermometer then it 
follows that the excess quartz in porphyries (phenocrysts) does not begin 
to be precipitated until the lava has cooled to 800°. From this and the 
great abundance and wide distribution of the resorbed quartz phenocrysts, 
it follows that the siliceous lavas probably rise to the surface very slowly— 
so slowly that the large quartz crystals may be precipitated and again 
resorbed while the lava which ultimately solidifies as a glassy rock has cooled 
to 800°. 
If calcite, pyrite, or some other common vein mineral should supply 
another point near 100° C., certain vexed problems related to the genesis 
of an important class of metalliferous deposits could easily be solved. 
Seventeenth Annual Report of the Ontario Bureau of Mines, 1908. 
Published by order of the Legislative Assembly of Ontario. 
TuHos. W. Gipson, Deputy Minister of Mines, Toronto, 1908. 
The report includes a statistical review of the mineral productions of 
Ontario for 1907, technological and geological notes on various mines 
by E. T. Corkill, a description of the geology of Thunder Bay—Algoma 
Boundary by Arthur S. Parsons, of the Iron Ranges east of Lake Nipigon 
by A. P. Coleman and E. S. Moore, and a review of the iron and steel 
industry of Ontario by George Cleghorn Mackenzie. 
The value of the mineral production for 1907 was $25,019,373 .00, 
an increase of 12 per cent. over 1906. Six metals yielded nearly fifteen 
million dollars. These, in order of their value, are silver, iron, nickel 
(ore value), copper, cobalt, gold. The non-metallic products yielded above 
ten million dollars. 
The splendid showing is due chiefly to activities in silver mining at 
Cobalt, which produced $6,301,095 .00 in silver, cobalt, arsenic, and nickel. 
