io SIDNEY POWERS 



The physiography and geology of Grand Manan divide the 

 island into two provinces: a western upland underlain by Triassic 

 basalt Hows, and an eastern lowland underlain by pre-Silurian 1 

 metamorphic rocks. The upland represents the level of the 

 Summit 2 peneplain, at elevations of 200-400 feet. The western 

 coast of the island is fronted by cliffs rising abruptly in an almost 

 straight line to a height of 100-300 feet. 



The Triassic rocks of the island consist of basalt flows under- 

 lain by purple shale. The shale is exposed to a thickness of only 50 

 feet, and this exposure is at Dark Harbour, on the western side of 

 the island. The basalts rest directly on older, metamorphic rocks 

 on the eastern side of the island; at Red Head, on the south, and 

 at the northwestern end of Flag Cove, on the north. At the 

 former locality the contact dips 35 degrees, suggesting a fault, but 

 the recent weathering of the rocks near the contact obscures the 

 exposure. 



The basalt flows are thick at the base and thin at the top. The 

 exact thicknesses are given below with the resume of the igneous 

 rocks. The dip of the flows is variable. At Dark Harbour it is 

 practically horizontal, but north of this place, the dip is down toward 

 the north at angles of 5 to 15 degrees. It is difficult to determine 

 the horizontal extent of any one flow. Diabase dikes are reported 

 by Bailey at several places, one of which is Swallow-Tail Light. 



The faults on Grand Manan are obscured by the massive 

 character of the basalt. The major fault bounds the west side of 

 the island, and the cliffs, which run in an almost straight line for 

 15 miles, mark the fault-line scarp. East-west faults are less 

 prominent. One may occur at Dark Harbour, as many of the 

 streams flowing across the Newark basalts follow fault-lines. Minor 

 faults are seen in the shore exposures. 



Split Rock. — Eighteen miles east of St. John, between Gardner's 

 Creek and Tynemouth Creek, there is a strip of Triassic sediments 



1 The age of these rocks is probably pre-Cambrian, as they are older than the 

 Silurian rocks of the Eastport Quadrangle. See E. S. Bastin, U.S. Geol. Survey, 

 Geol. Atlas, Eastport Eolio (No. 192) (1914), p. 14. 



■"The term "Summit" peneplain is used instead of "Cretaceous" peneplain in 

 order to avoid any reference to the age of this topographic feature. 



