1913.] NATURAL SCIENCES OF PHILADELPHIA. 597 



The total thickness of this division is upwards of 2000 feet or more, 

 and of this more than half is below the lacustrine flint layer; the 

 bottom of the formation is hard to define, as it is not easily dis- 

 tinguished from the bedded deposits of the basal igneous complex. 

 But of the distinctly bedded deposits, which are exposed in many 

 places and always with the same general north or northeast dip, 

 the thickness must be at least 2000 feet. The division is composed 

 of the volcanic material of the igneous basement, reworked by water, 

 and water deposited; mixed likely with other volcanic material 

 which, erupted during the deposition of these beds, fell into the 

 water, and was distributed on the sea bottom. 



As indicated above, these tuff beds, with their included marls and 

 cherts, appear to pass upward into the marls and limestones of the 

 Antigua formation without any stratigraphic break, or the Antigua 

 formation rests conformably upon them. At several places along 

 the contact of the marls with the tuffs and shales shallow wells 

 have been sunk for water, and while the contact of these two forma- 

 tions is seldom exposed, the conformable character of it is indicated 

 by these diggings. When the Antigua formation itself is found well 

 exposed near the contact, the dip of the marls is about the same as 

 that of the tuffs, and is in the same direction; that is, the marls are 

 found to dip gently at 10°-12° to the northeast in the same way as 

 the tuffs. There is certainly no indication of a fault separating the 

 two formations as suggested by Mr. Guppy. The fossils of the 

 included marls and cherts, interbedded with the tuffs and shales, 

 do not indicate any other age than Oligocene, which is the age of the 

 Antigua limestone as indicated by its fossils. But the species that 

 have been observed in the Antigua limestone are only in part the 

 same as have been determined from the tuffs and included marls 

 and cherts. These tuffs were, in part at least, shallow water forma- 

 tions; mud cracks and even ripple marks were observed by me in the 

 tuffs underlying the lacustrine cherts, and the presence of these 

 fresh-water deposits (the lacustrine cherts) indicates land at this 

 time. The tuffs may have accumulated rapidly when they are 

 €oarse in grain, as these volcanic conglomerates which underlie the 

 fresh-water deposits, but the finer material of the thin-bedded tuffs 

 which overlie this horizon were probably slowly deposited and in 

 water of greater depth. This was likely the case with the marls of 

 the Antigua formation also, in great part; although some of the 

 harder limestone beds of this deposit have the appearance of coral- 

 reef material. 



