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with the basal McAdam limestones here forming a low 

 anticlinal. At low tide the fault line is well shown, the 

 shales on one side and the limestones on the other serving 

 to make it very prominent, but at high tide it can not be 

 seen. Beginning at the fault is the broad cove extending 

 to Arisaig point. Its existence is determined by the readi- 

 ness with which the Ross Brook shales yield to erosion. 

 The upper half of the exposures is made prominent by 

 the high cliffs of green shales, but in the lower half the 

 cliffs are less high and steep. The lenticular beds of sand- 

 stone which are scattered through the shales make dis- 

 connected shelves across the cliffs and their varying 

 thickness is excellently shown. In the green shales it is 

 possible to collect fossils anywhere, but perfect specimens 

 do not commonly occur. A good black shale fossil locality 

 begins about 125 yards (114 m.) west of the mouth of 

 Arisaig brook and extends to its east bank. 



Arisaig point is formed of the upturned edge of the 

 rhyolite flow at the base of the Silurian which, together 

 with the amygdaloid by which it has been intruded, forms 

 with a few interruptions, the shore for the next three miles. 



The Beach Hill cove formation is so poorly exposed at 

 Arisaig point that it is not possible to adequately examine 

 it To see it in its completeness Beech Hill cove or Doctor's 

 brook must be visited. The former locality is about three 

 miles east of Arisaig point and is best reached by way of 

 the shore road. There the beds are steeply upturned 

 and form a sloping shore which at no place rises to a cliff. 

 At Doctor's brook the beds of the Beech Hill cove forma- 

 tion form the cliffs below the shore road bridge and the 

 same structural relations obtain as at Beach Hill cove. 



DESCRIPTION OF THE GEOLOGICAL SEQUENCE. 



The sequence of the strata in the Arisaig region begins 

 in the Lower Ordovician and with many interruptions 

 extends perhaps to the Pennsylvanian. Excepting the 

 glacial and stream gravels there are no deposits later 

 than the Pennsylvanian. 



Ordovician, Brown's Mountain Group. 



The oldest rocks of the region have been described as 

 the Brown's Mountain group, a name proposed by Will- 

 liams. On lithological grounds the group has been divided 



