t 
20 
MUSEUM BULLETIN NO. 2. 
the writer obtained his results by calculation, taking into 
consideration the slope of the hill as well as the dip and strike 
of the sills. 
The St. Mary Sills . — Intruded into the westerly dipping 
Aldridge quartzites, which form the mountains rising on both 
sides of St. Mary lake, is a series of gabbro sills which were 
studied in some detail. Sill “A” (see Figure 4), which apparently 
represents the highest one in the series, is 140 feet thick and 
*?*•> 
Sc4le 
Fig. 4. Natural section of the St. Mary Sills. 
contains an upper granite (micropegmatite) zone of specific 
gravity, 2-76, 70 feet in thickness, passing gradually downwards 
into a gabbro of specific gravity 3-01, also 70 feet thick. Separat- 
ing sill A” from sill “B” occurs 400 feet of argillaceous quartz- 
ites. Sill B, which is 985 feet thick, is composed almost 
entirely of hornblende gabbro. It is in this sill the hypersthene 
gabbro occurs which shows the transformation of augite and 
hypersthene into hornblende. No granitic (micropegmatitic) 
zone is present in this sill although here and there in the centre 
