280 THE VEEMILION IKON-BEAEING DISTRICT. 



tions of tbe distribution of the other formations, that the structure of the 

 series has been determined. It may be noted here that in the absence of 

 any striking key rocks the folds in the slates were determined chiefly by 

 the distribution of the slates and their variation in strike and dip. 



The general strike of the slate beds is N. 80° E. The slates have 

 been very closely compressed, and consequently many of the exposures 

 show the most intricate plications. On the large folds, as well as on the 

 plications, the strikes extend varyingly to nearly every point of the compass, 

 the direction depending on the position on the fold of the place where the 

 strike is taken. The dips are high and range from about 70° S. to 70° N. 

 The northern dip is the more common and is generally not far from 80°. 

 The axes of the folds trend approximately N. 80° E., and, as shown by the 

 predominant northward dip of the beds, the axial plane of these folds is 

 generally overturned, dijoping slightly north. In addition to a south- 

 north compression — to be exact, the pressure came from a direction slightly 

 west of north' and east of south — producing the folds trending east and 

 west, there has been pressure at right angles to this, which caused a 

 corresponding development of north-south folds. As a result of this minor 

 cross folding, the axes of the major folds — the folds trending east and 

 west — have a pitch varying from 90° to 65°. As a result of the 

 compression, several sets of joints have been formed in the rocks. One 

 trends from N. 60° to 80° E., in close agreement with the strike of the 

 bedding and with the trend of the axes of the folds. Another set is 

 nearly at right angles to the above, and varies from north and south to 

 N. 10° W. The joints, however,' evidently bear definite relations to the 

 folds, having been produced by the same forces that caused the folding, for 

 as the strike of the beds varies upon the folds the joints vary also. Thus 

 on the point southeast of Sucker Point, where the beds strike N, 50° W., 

 the joints strike N. 80° W. and N. 30° E. The close compression of these 

 slates has produced a fissility which is veiy uniform throughout the region. 

 It is very noticeable in the slates, and its general strike is N. 80° E., 

 although a variation of a few degrees to south or north can be found. In 

 general, there is an agreement of the strike of fissility and bedding, but, as 

 Van Hise has demonstrated," the fissility bears diiferent relations to the 



« Principles of North American pre-Cambrian geology, by C. E. Van Hise: Sixteenth Ann. Eept. 

 U. S. Geol. Survey, Pt. I, 1896, pp. 656-659. 



