366 PRE-CAMBRIAN NORTH AMERICAN LITERATURE 
bedded with the limestone, while many of the latter have the appearance of 
interbedded members, and others closely resemble somewhat modified intru- 
sions. Wherever the hornblendic and pyroxenic gneisses appear, they show 
a great amount of crumpling and crushing, which goes from slight plication 
to elaborate contortion or to crushing into angular fragments ina paste of lime- 
stone, thus producing remarkable breccias. In all of these cases the lime- 
stone shows little or no sign of structural change, having the appearance of 
a plastic mass in which the contained layers could be twisted to any extent. 
It therefore follows that the massive and undisturbed appearance of the lime- 
stone, when free from gneissic layers, does not show that it has not been sub- 
jected to intense mechanical strain, as subsequent to this it may have recrys- 
tallized. 
This limestone series has a marked resemblance to the Grenville series, 
but because it is difficult to establish such an equivalency, it is suggested that 
it be called the Oswegachie series. The areas between the belts of limestone 
are occupied by gneiss, whose origin and relations to the limestone series is 
doubtful. The limestone series can hardly be regarded as of other than sedi- 
mentary origin. In many cases these gneisses adjacent to the limestone 
closely resemble the interbedded garnetiferous gneisses, and doubtless should 
be regarded as members of the limestone series. These varieties pass gradu- 
ally into more nearly massive gneisses of feldspathic aspect, and these are in 
a number of cases in direct contact with the limestone. A part of these 
gneisses at least are of igneous origin, as is shown by their contact relations, 
but whether this explanation is applicable to them all it is impossible to show. 
Intrusive in the limestone series are granite, diorite, gabbro, and diabase. 
Their intrusive nature is shown by all the usual phenomena characteristic of 
such relations. 
The gabbro is most variable in its petrographical character. At one place 
it is in sharp contact with the granite. The relations of the gabbro to the 
gneiss are difficult to unravel. At Natural Bridge is found the normal gabbro, 
and in passing toward the red gneiss it appears to grade into it, and the two 
may be different facies of the same eruptive mass. The contact zones between 
the limestone and the intrusive gabbro are narrow and sharply defined, and 
this fact, combined with the great mechanical disturbances of the limestone 
series, justifies the conclusion that its metamorphism is largely dynamic. 
Kemp* describes the crystalline limestones, ophicalcites and associated 
schists of the eastern Adirondacks. Study of the region seems to cor- 
roborate the conception of the Adirondack Mountains, as sketched by Van 
Hise, as a central intrusion of igneous rocks, with a fringing rim of older 
gneisses, schists, and limestones. A closer approximation would be to regard 
*Crystalline Limestones, Ophicalcites and Associated Schists of the Eastern 
Adirondacks, by J. F. Kemp, Bull. Geol. Soc. Am., Vol. VI., 1895, pp. 241-262. 
