262 



altered by the proximity of the trap. No clear intersections of 

 these large masses of diabase by the smaller dikes of the 

 district liave been observed ; and perhaps the most probable 

 view is, that some of the smaller and more typical dikes 

 are offshoots from these great intrusive masses. One thing is 

 certainly very clear; viz., that the latter occur where the 

 stratified rocks show exceptional disturbance, and hence 

 probably date, like the smaller dikes, from the period when 

 the strata Avere folded and faulted. 



The three dikes on Langlee Island appear to agree in hading 

 N. 10°— 15°, but while the north dike and the south dike are 

 parallel with the strike of the conglomei'ate, trending a little 

 north of east, the middle dike is oblique to the strike, 

 trending a little south of east. The latter dike is highly 

 altered, appearing to be made up very largely of secondary 

 minerals — epidote and quartz. These dikes can not be 

 identified on the main land, passing, probably, beneath the 

 drift of Crow Point. The numerous dikes in Melville Garden 

 and Planter's Field and on the shores of Huit's Cove evidently 

 belong mainly to the south-of-east system, but the outcrops are 

 not easily connected, with the single exception of the large 

 dike which follows the general course of Grove Avenue, and can 

 be traced in frequent outcrops for 1,800 feet. The very unusual 

 trend of this and one or two other dikes may, perhaps, be 

 due in some way to the northerly strike of the strata. The 

 nearly north -south dike in the main belt of slate appeal's, at 

 first glance, to belong to the third or newest system of Nan- 

 tasket. Lithologically, however, it does not agree with that 

 system; and it seems best to regard it as, normally, an 

 east-west dike which has been influenced in its trend by the 

 bedding of the slate. 



Dikes of Slate and Grape Islands. 



About twenty dikes from 2 to 8 feet wide have been 

 observed on Slate Island- Fully two thirds of these are 



