THE ACADIAN TRIASSIC 263 



In' each locality there are several flows, indicating successive 

 extrusions within such a short time of each other that no sediments 

 were deposited between the flows. It is impossible to state whether 

 any single flow originally covered the geographical area over which 

 the remaining exposures indicate that the formation once extended. 

 The Palisade diabase formes one sill 100 miles long on the out- 

 croping edge, while North Mountain is 120 miles long. In the 

 former case the igneous material was intruded at some distance 

 below the surface and had to push up this great weight of rock, 

 which, however, acted as a blanket over the feeder. In the latter 

 case the igneous material was extruded at the surface, with no 

 roof to sustain, but the feeders were constantly subjected to the 

 great heat loss by radiation at the surface, which would tend to 

 freeze them up. 



Dikes associated with the North Mountain basalt are rare. 

 Several were reported on Grand Manan by Bailey, 1 but they were 

 not observed by the writer. The largest of these is 50 feet wide, 

 and occurs at Flag Cove, near Swallow-Tail Light. 



Other narrow dikes occur on the south side of Scots Bay, just 

 east of the Scots Bay formation exposures. These dikes cut the 

 basalt within 25 feet of the top of the upper flow. From the other 

 exposures of this flow it is judged to be at least 100 feet thick, and, 

 if so, it is quite evident that the dikes cut the upper flow and are 

 not the feeders. With the dikes are many fissures filled with vein 

 material which is seen under the microscope to consist largely 

 of silica stained red with hematite. The width of both the veins 

 and the dikes varies from one to ten inches, and in the field they 

 look very much alike. 



In thin-section the dikes are seen to consist of a very fine-grained 

 diabase, greatly altered and stained with limonite. The rock is 

 similar to that of the flows near the center, but shows some glass. 



From the field evidence of the dikes and veins side by side in the 

 upper part of this thick flow, and from the microscopic evidence, 

 it is concluded that the dikes were formed from the basalt of the 

 upper flow after the crust of the flow had solidified and while the 



1 L. W. Bailey, Geol. Surv. Canada, Report of Progress, 1870, pp. 216-21. 



