Correspondence. 213 
limestones in the United States for which a Laurentian age had been 
claimed, had, on further examination, been found to be primordial 
[¢. e., Cambrian}. 
This, I think, can hardly be the case with the St. John limestones. 
The earthy (cryptocrystalline) condition of some of these limestones 
is apt to mislead those who expect to find Laurentian limestones (or 
perhaps I should say pre-Cambrian limestones) always coarsely crys- 
talline. Hence Sir Wm. Logan, when he came here (about 1870) fresh 
from the survey of the limestones of the Ottawa valley, was surprised at 
the modern aspect of those near St. John. Dr. T. Sterry Hunt also, 
after his studies of the pre-Cambrian rocks of New England and the 
maritime provinces of Canada, classed these limestones in his Lower 
Taconic, below the Cambrian. Their comparatively unaltered condition 
is shown by the numerous carbonaceous bands, called, locally, “blue 
limestones,” which are intercalated in certain parts of the terranes. In 
fact there are not only carbonaceous, but bétwmdnous limestones present 
in this series, and this is shown by the fact that they give off a distinctly 
bituminous odor when struck with a hammer. This, however, is not an 
isolated fact, because a limestone in the Archiean tract of Scandinavia 
has been shown to contain bitumen, I think as high as 5 per cent. It is 
difficult to conceive of the introduction of this substance into a series 
of sediments except through the agency of organisms of some kind. 
Such we know to have been the source of bitumen in the rocks of later 
ages, and we naturally seek thus to account for its presence ia these old 
limestones. 
And yet, though in certain places these limestones show compara- 
tively little alteration, they exhibit everywhere a secondary crystalliza- 
tion, often strongly pronounced, and not infrequently giving rise to 
highly crystalline, calcareous masses; the preservation of any organisms 
which may have been associated with the production of these limestones 
is therefore not only uncommon, but seemingly local. 
Although comparatively modern in aspect, these limestones are no 
doubt pre-Cambrian, for the following reason: Subsequent to the pro- 
duction of the series of which they form a part, a great extrusion of 
igneous rocks (volcanic ash, scoria and mud) occurred in this district. 
These were piled up toa great thickness and spread over a wide tract 
of country; yet their thickness appears to have been very irregular, or 
denudation before Cambrian times swept away large masses of them, so 
that the underlying limestone series was brought near, or quite to the 
surface in some places. 
The Cambrian rocks themselves have a clear foundation in certain 
conglomerates which overlie the volcanic series and show themselves 
along the borders of the Cambrian basins. These conglomerates are 
usually made up of fragments of the volcanic series, intermingled with 
quartz pebbies, but at one locality in the city of St. John, where the 
Cambrian rocks are in close proximity to limestone ridges, pebbles of the 
limestone are mingled in the conglomerate with those of the volcanic 
series, hence we cannot doubt that these limestones were hard rocks, 
