Page:Popular Science Monthly Volume 43.djvu/265

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ous period, the bay was much, wider and somewhat longer than it is now. The long ridge of trap rock, known as the North Mountain, which stretches as a huge wall between the Annapolis Valley along its southern, and the waters of the bay along its northern base, did not then exist, and the waters of the bay extended uninterruptedly over the whole of the Annapolis Valley to the base of the Silurian hills which, under the name of the South Mountain, now form the southern inclosure of the valley. Eastwardly the head waters of the ancient bay washed the Devonian and Carboniferous rocks of the Cobequid Hills, while the northern shore line of the present bay, skirting the southern limit of the Palæozoic rocks of New Brunswick, is substantially identical with that of the original bay.

In general character the tidal movements of this larger Atlantic inlet were the same as in the smaller modern bay. And the semidaily ebb and flow of the waters produced, by their incessant attrition with the carboniferous limestones, shales, and sandstones, and the other ancient rocks that formed the bed and margins of the bay, immense quantities of sand and mud—sediment that was redistributed over the greater part of the Fundy Valley. Subsequent changes of level caused a recession of the waters to within their present limits, and brought to view, as the Triassic, or new red sandstone, extensive areas of these deposits. These red sandstone strata are still to be seen in shreds and patches at various points in the Annapolis Valley and on the shores of the Minas and Annapolis Basins. Their general dip toward the north indicates that the epoch-closing movement which narrowed the Bay of Fundy within its present confines was a sinking of the bed along its northern or New Brunswick border.

Following this subsidence, and as the concluding events in the series of seismic convulsions by which the region gained its present topographical features, occurred the volcanic eruptions in which the North Mountain had its origin. This long, trappean wall forms the southern boundary of the bay from Cape Split to the extremity of Digby Neck, a distance of one hundred and twenty-five miles, the only interruption to its continuity being the singular gap called Digby Gut, which gives an entrance into the beautiful Annapolis Basin. Though there were probably many volcanic vents along this extended line of fracture, yet the scene of greatest activity was undoubtedly near Cape Split, at the entrance to Minas Basin, scattered along the shores of which on either side are isolated patches of amygdaloidal trap. Transverse ridges of the same volcanic rock run at intervals, also, across the bottom of the bay.

It is the grinding action of the Fundy waters upon these two Triassic rocks, the trap and its underlying sandstone, that provides