28 The American GeologisL July, 1895 
On the south side of the bay siniihir shaly limestones were 
noted overlying a black calcareous rock. Further south the 
stratified rocks have been disturbed by the intrusion of Owl's 
head. The sediments are somewhat metamorphosed to cal- 
careous schists and talcose slates. In this region calcareous 
layers were recognized beneath black slaty deposits, while on 
the east the calcareous rocks were found to invariably overlie 
the slates.* At Round island the rocks are made up wholly 
of calcareous schists intersected by dikes. These rocks are 
probably metamorphosed portions of Upper Silurian deposits. 
The Dikes. 
Through the entire area examined the dikes were found to 
cut the shaly limestones. It seems probable that the outlying 
dikes are more or less closely associated with the intrusions 
now represented by Owl's head, mount Orford, and possibly 
many others known to have occurred even as far north as 
Montreal. The dikes represent two well defined groups, 
yranitca and lamprfrphnreK. 
Granife Dikes. 
The granitic intrusions are invariably light in color, owing 
to the predominance of quartz and white or tiesh colored feld- 
spar. The dark silicates consist mainly of biotite, with occa- 
sional flecks of muscovite, and yellowish brown patches of 
some mineral substance which has probably resulted from the 
decomposition of an iron-bearing silicate not at present re- 
cognizable. In some instances the crystalline texture becomes 
*Im ii priviilc letter Mr. R. W. Ells of tlie Canadian Geolofiical Survey 
has kindly outlined the results derived from a recent study ot the strat- 
igra[)hy of Ihis region. He says: "The lower part, as you suppose, is 
bordered on either side by I'pper Silurian limestones which contain 
fossils at several points. These rocks extend from Cu[)i. Gully"s wharf, 
north of Majioon's ])oin(, to Mago<;', and on the westside from the north 
entrance of Sar<;ent"s bay to the north end of the lake At Owl's head 
th(! Upper Silurian is undiM-neath the Cambro-Siluriaii firaptolilic 
slates, the formation being overt urned. At Round island, below the 
Mountain house the rocks are Upper Silurian, fossiliferous, now altered 
to schists and cut by dikes from the Owl's head. This ])laces the agi> 
of the Owl's head and other prominent hills in th»> vicinity at the same 
horizon as the Montreal intrusion oi' at the close of the I'pper Silurian. 
The Owl's head dikes also cut the ("ambro-Silurian slates as do the Or- 
ford diorites on the east. On the east side of the lake the Georgoville 
limestones are underlaid by the graptolitic slates about one and a half 
miles south of the village and the ridge between there and Fitch bay 
consists of an intermediate series, presumably Cambrian, between the 
graptolitic series and the pre-Cambriaii of tlu' extension of the Sher- 
brooke anticlinal. 
