1913.] NATURAL SCIENCES OF PHILADELPHIA. 593^^ 



water chert; F, Upper tuffs. They have been placed together by 

 Spencer as one group of deposits, and while it may be possible locally 

 to recognize the divisions made by Purves, the cherty limestones 

 of marine origin, and possibly also those of fresh-water origin, are in 

 more or less lenticular deposits and not continuous. The division 

 D of Purves, "Volcanic sands and sandstones," is locally developed 

 and underlies in some places the fresh-water cherts or the layer 

 containing the fossil wood, but it does not differ very much in appear- 

 ance from some phases of B, the lower stratified tuffs. This division 

 B of Purves, the lowest member of this group of deposits, is found to 

 the west of the Central Plain, and well developed along the southern 

 shore of St. John's Harbor. The beds have the appearance of a 

 buff-colored sandstone, but on close examination the fragments of 

 which it is composed are seen to be angular, not water worn, and 

 to consist of volcanic rock and feldspar. These lower beds maj^ have 

 a higher dip than those of the Central Plain — 20°-30°, as against 

 12°-15° — and the dip is more to the north in many cases. But as the 

 higher rocks in this lower series of tuffs are encountered, the dip 

 diminishes and becomes more northeast. At the level of the lower 

 limestone and marine chert as seen just to the south of St. John's 

 (about a mile south of the town) the tuff becomes almost white 

 from admixed kaolin, and has this lower dip of 12° N. E. It is in 

 some places, soft, in others hard and compact, and almost pure white 

 except for black specks of magnetite. This magnetite forms black 

 layers on many of the recent sea-beaches and consists of octahedral 

 crystals and angular fragments of crystals. The limestone deposit, 

 which in places is altered to a flint or chert, contains corals, those 

 from the Nugent collection in the possession of the Geological Society 

 of London have yielded the following species (Duncan) :^° 



Astrwa cellulosa var. curvata Duncan. 



Astrcea megalaxona Duncan. 



Astrcea antillarum Duncan. 



Solenastroea turonensis Mich. 



Isastrcea conferta Duncan. 



Isastrcea turbinata Duncan. 



Stephanocce7iia tenuis Duncan, also found in the lower tuffs. 



Coeloria dens-elephantis Duncan. 



Astroria polygonalis Duncan. 



Astroria affinis Duncan. 



Astroria antiguensis Duncan. 



Astroccenia ornatd Ed. and H. 



Alveopora dcedala Blainv., also vars. regularis and minor. 



Styloccenia lobato-rotundata (Mich.). 



10 Quart. Jour. Geol. Soc. London, Vol. XIX, 1863, p. 477. 



