262 SIDNEY POWERS 



thickness. A similar ash-bed is exposed west of Swan Creek under 

 the agglomerate flow mentioned below. The thickness of the flows 

 on Gerrish Mountain may be considerable, as the basalt covers 

 a large area. 



The agglomerate beds, with associated tuffs, are exposed from 

 Greenhill eastward to Five Islands, in disconnected areas. The 

 relation of these remnants of flows and volcanic ejectamenta to 

 the sandstones is a problem only partly solved because of the faulted 

 contacts, with possibly minor thrust-faults, and the landslides which 

 are especially abundant in the tuff. The tuff underlies the agglom- 

 erate in most cases. The thickness of the tuff varies from a few feet 

 to 50 feet, and that of the agglomerate flows from 20 to 150 feet or 

 more. Exposures show that the agglomerate is overlain by red 

 sandstone, and is therefore older than the North Mountain basalt. 



The agglomerates consist of a mass of angular fragments of 

 basalt and amygdaloid in a dark-green matrix of a basaltic com- 

 position. The exact character of the matrix is difficult to determine 

 because it is everywhere so badly weathered that a solid specimen 

 could not be procured. The field evidence, however, indicates that 

 this matrix is in part tuffaceous and in part a normal basalt. At 

 the sides of some of the masses of agglomerate are blocks of angular 

 basalt and amygdaloid imbedded in a red sandstone matrix, showing 

 that the breccia was either blown out into the area where sandstone 

 was being deposited, or washed out from a bed of tuff and breccia. 

 The cross-cutting contacts at one side of the masses of agglomerate 

 in two instances give them the appearance of intrusive bodies 

 rather than of flows. If the agglomerates are intrusive, rather 

 than extrusive, they probably fill volcanic necks. 



NORTH MOUNTAIN BASALT 



Under the term North Mountain basalt, used in a generic sense, 

 are included the basalt flows of Grand Manan, Isle Haute, Cape 

 d'Or, Cape Sharp, Partridge Island, and North Mountain. The 

 series of flows at these localities are correlated either for structural 

 reasons or because they are underlain by shale correlated with the 

 Blomidon shale. 



