234 Wal WOOKINAIL OF (GIS OLOGM, 
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an approximate thickness of 1300 feet, and in some localities there 
may be 2000 feet of strata in the series. 
The lower series of Algonkian, called the Mount Holly series, is 
contrasted with the Mendon series in nearly every way. he structure 
of the series is so complicated, the different rock types vary so greatly 
and the series has been subjected to such a multiplicity of dynamic move- 
ments, that no definite stratigraphy has been made out. Some of the 
prominent rocks of the series are biotite-schist, muscovite-schist, gar- 
netiferous schist, vitreous quartzite, augen-gneiss and various kinds 
or limestone: “Phe limestones are in) irregular Wensesyvandsvane 
extremely local. There may be two horizons of limestone or a dozen. 
The series, because of the undoubted areas of sedimentary rocks which 
have escaped destruction, are regarded as clastic. Associated with 
the above rocks are very abundant schistose, igneous rocks, comprising 
both dikes and sheets. 
The two series of Algonkian rocks are regarded as unconformable 
for the following reasons: Between the two there is a great lithological 
difference ; the Mount Holly series has been cut through by eruptive 
rocks in a complicated fashion, and these do not occur in the Mendon 
series; the Mount Holly series is folded in a much more intricate 
manner than the Mendon series, and secondary structures have devel- 
oped to a far greater degree; at the bottom of the Mount Holly series 
is a widespread formation of conglomerates and gneiss. ‘The schis- 
tosity of the two series is parallel, but this is regarded as due to dis- 
integration before the Mendon series was deposited, and to post-Men- 
don folding. 
Smyth, C. H.,* gives a petrographical description of the gabbros of 
the southwestern Adirondack region, and of black hornblende-gneiss 
which occurs in the same area. The most altered form of the gabbro 
is very similar to the hornblende-gneiss, and it is suggested that the 
latter is but an extremely metamorphosed phase of the former. 
Smyth, C. H.,? describes a group of diabase dikes as breaking 
through the granite, gneiss and quartzite in the vicinity of the village of 
Gannanoque, Ontario, the whole being overlain by Potsdam sandstone. 
* Gabbros in the Southwestern Adirondack Region, by C. H. SMyTH, Jr., Am. Jour. 
Sci., Vol. XLVIII., No. 283, pp. 54-80, July, 1894. 
2A Group of Diabase Dikes among the Thousand Islands, St. Lawrence River, by C. 
H. SmMyTH, Jr. Trans. N. Y. Acad. Sci., Vol. XIII., Sig. 14, pp. 209-214, August, 1884. 
