THE LEYDEN ARGILLITE. 2(J 1 



in diameter and parallel, which suggest scolithus, but which are parallel to 

 the bedding. 



All these specimens were submitted to Mr. C. D. Walcott and other 

 paleontologists, but they could not decide that any of them were certainly 

 of" organic origin. 



THE LEYDEN ARGIIiLITE. 



DESCRIPTION. 



The rock is in its whole extent of uniform texture and structure — a 

 dark-gray and very fine-grained slate with glistening cleavage surfaces, 

 dull-black when broken across the ends, and generally crumpled and corru- 

 gated to the extreme of complexity. It is remarkably barren of all acces- 

 sory minerals, and this has been taken as a characteristic to distinguish it 

 from the Conway schists, though in places small garnets and biotite scales 

 ai-e scattered sparingly over its cleavage surfaces. Slaty cleavage is devel- 

 oped in it in every degree. Thin sandy layers often show the original 

 bedding after the rock has been crumpled up into sharp folds and the 

 cleavage perfectly developed outside these layers, and the rock can still be 

 separated along these into thick plates fluted and folded in the sharpest 

 curves, and at the ends of the plates the slaty cleavage is seen to cut across 

 the slab and to divide it into thin, flat laminae regardless of its convolutions. 

 Moreover, the importance of the shearing force in the development of cleav- 

 age can often be beautifully seen, the fine, close-set and equidistant conju- 

 gations becoming sharper and changing from folds into faults, and the 

 elements between these faults being flattened out, with some degree of flow 

 of the material, into the cleavage plates. 



A remarkable block found (not in place) at the outcrop nearest and to 

 the west of the lower quartzite of the Williams farm in Bernardstou may 

 find mention here. A mass of chlorite-slate 3 inches wide cuts across the 

 argillite exactly like a dike. It is bounded by parallel planes and is sharply 

 demarcated from the ai-gillite, and while both are cleaved perfectly at right 

 angles to the plane of the dike, the plane of cleavage in the green schist 

 makes a small angle with that of the argillite. One can not well avoid 

 surmising that a small diabase dike has been here very curiously metamor- 

 phosed, but the microscope shows only matted chlorite and muscovite scales, 

 quartz, and geniculate rutiles, the latter xisible also with the lens. 



