3o6 



to green and black. The time of the extrusion was pre- 

 Arisaig and since fragments of a similar rock occur in the 

 Malignant Cove conglomerates it is probable that it was 

 antecedent to the deposition of that formation. 



Elsewhere in the Arisaig district are outcrops of rocks 

 which Williams has called acid intrusives, consisting of 

 dark colored rhyolite and quartz porphyry, the outcrops 

 finding their greatest physiographic expression at Sugar 

 Loaf hill (rhyolite) south of Malignant Cove and McNeil's 

 mountain (quartz porphyry), just south of the Sugar 

 Loaf hill and one of the highest points of the area. Assoc- 

 iated at one or two localities are rhyolite flow breccias. 

 The intrusions are in the form of dykes and larger masses 

 which Williams has described as necks and cut either the 

 James River and Baxters' Brook sediments or the James 

 River granites. The available evidence points to their 

 formation during the same phase of volcanic activity 

 in which the rhyolite outflow at the base of the Silurian 

 occurred. Also in the Malignant Cove — Sugar Loaf area 

 are tuffs and breccias which are apparently interbedded 

 and contemporaneous with the James River slates. 



In the shore cliffs there are no rocks more conspicuous 

 than the black dykes of amygdaloidal diabase or 

 basalt. These cut all the strata except those of the 

 Ardness and Listmore formations and are themselves 

 cut by the red dyke. The intrusions are in the 

 form of dykes and sheets and some may be flows. The 

 largest observed intrusion begins at Arisaig pier and extends 

 eastward for about three miles, but most of them do not 

 have a width exceeding lOO feet (30 m.). The intrusions 

 are all of one age as no diabase was seen to cut diabase. 

 The fact that neither the Ardness nor the Listmore forma- 

 tions are cut by these dykes suggests that the time of the 

 intrusions was pre-Ardness but it does not necessarily 

 follow that this view is correct as there may not have been 

 intrusions in the localities of the present outcrop of these 

 rocks. The red dyke resembles a shale and on the basis 

 of unpublished chemical analyses was considered such 

 by the writer, but after more extended study, Williams 

 is inclined to regard it as an intrusion. It cuts the diabase 

 and may have been intruded during a later phase of that 

 period of igneous activity. 



