220 C. D. WALCOTT PRE-CAMBRIAN FOSSILI FERGUS FORMATIONS 



Fe&t 

 Green, 2)nri:)le, pinkisli, or red slates in frequent alternations ; the texture of 

 these slates is p;enerally extremely fine, and in some cases they approach 

 in hardness to jasper or chert ; the fracture is often conchoidal, and the 

 imperfect cleavage parallel with the bedding, but in many instances the 

 rock has a good cleavage, oblique or at light angles to the stratificatf5n, and 

 is well adapted for roofing purposes ; the exposed surfaces weather for the 

 most part to a yellowish white; the fossil forms, su^oposed to be of the 

 genus Oldhamia, were found in these slates toward the top 3,300 



Conception slates. — The various members of this formation are well 

 shown at Topsail Head and at the head of Conception bay ; also on the 

 eastern side of Placentia bay. 



Feet 



1. Slate conglomerate and slate without pebbles, the matrix of the conglom- 



erate chiefly of a dark greenish color and trappean aspect, inclosing 

 pebbles of quartz, many of which are white and some gray, syenite, red 

 and brown jaspers, slate, and occasionally drab-colored or yellowish 

 chert; vertical cleavage sometimes observable, and at times cutting in- 

 differently through both pebbles and matrix, while at other times the 

 pebbles ai-e loosely imbedded and break out whole from a blow of the 

 hammer 1 ,050 



2. Diorites, quartzites, and jaspeiy bands ; some of the latter of a reddish 



color, with hard greenish slates ; at Topsail there is probably some addi- 

 tional lower strata, and there is one very remarkable stratum or vein 

 of vitreous white quartz, which runs parallel with the stratification 

 and exposes a thickness of from 10 to 12 feet, but may be more, the un- 

 conformable rocks occupying the margin between it and the shore. . . . 1,300 



AGE OF CAMBRIAN BEDS RESTING ON A VALON TERRANE 



The red and green slates near the base of the Cambrian section on 

 Manuels brook carry the Olenellus fauna. Mr G. F. Matthew* is in- 

 clined to consider that some of the fossils found in the red and green 

 slates below this horizon on Eandoni sound are pre-Olenellus and of pre- 

 Can^brian age. I do not think, however, that the published data are 

 sufficient to prove that such is the case. Reference to this will be found 

 in the discussion of the fossils found in pre-Carabrian rocks. 



UNCONFORMITY BETWEEN A VALON TERRANE AND CAMBRIAN 



Location and character of contacts. — As shown by the geological map of 

 the peninsula of Avalon, 1881, the Cambrian rocks do not come in con- 

 tact with the upper formations of the Avalon terrane. On the shores of 

 Conception bay they rest against the Conception formation at the base 

 of the' Avalon terrane and overlap onto the Archean. About Saint Marj^s 

 bay they are in unconfo-rmable contact with the Conception, Torba}', and 



* Trans. New York Acad, of Science, vol. xiv, 1895, p. 107. 



