358 Canadian Record of Science. 
mediately under or overlying them have been seen. There 
is little doubt, however, that they occupy either the summit 
of the Silurian or the base of the Devonian limestones. All 
the evidence that we have on the point has not as yet been 
perfectly elaborated, but it consists in the general horizon- 
tality of the beds wherever seen throughout the whole area, 
and in the existence of limestones holding fossils on Lake 
Manitoba, twelve miles distant in a south-westerly direction, 
and of limestones holding fossils on Lake St. Martin, eleven 
miles distant in a south-easterly direction. Also reference 
might be made to the above-mentioned bore on Vermilion 
River, where the gypsum was at the base of a bed of 
Devonian limestone one hundred and thirty feet in thick- 
ness. Thus these deposits are practically of about the age 
of the Onondaga Formation of New York and Western 
Ontario, in which rocks plaster-quarries have been worked 
for many years. This Formation also contains the great 
salt deposits of Ontario, and it is a significant fact, that a 
short distance to the west of the area under consideration, 
around the shores of lakes Manitoba and Winnipegosis, 
many brine springs are known to occur. In the State of 
Michigan, many of the plaster-quarries are also in rocks of 
about the same age. In Nova Scotia, the gypsum deposits 
are of lower Carboniferous age, and in Iowa they are stated 
to belong to a still higher horizon. 
The general hilly and irregular character of the surface 
underlain by the plaster beds, and the fact that isolated 
hills of gypsum rise above the surface of the otherwise 
level plain, make it appear probable that the deposits occur 
as lenticular masses in the beds of limestone wnich seem to 
compose the general floor of this whole area, though in 
most places the limestone is covered either by a mass of 
glacial till, or by the alluvial deposits laid down on the 
bottom of the ancient Lake Agassiz. The gypsum also 
resembles the limestone in being clearly stratified 
horizontally or at a very low angle. Besides this,some of 
the limestone of Northern Manitoba contains a large 
amount of sulphur scattered throughout its mass in the 
