MIDDLE AND UPPER ORDOVICIAN. 205 



SO that the point at which the exact Une of division between the two formations 

 occurs is scarcely indicated." Above division B Logan ^^^'^ gives C and D, as quoted 

 below, and according to Ami "'' certain fossils (Ecculiomphali) cited from division 

 C suggest the " Calciferous." The line between "Calciferous" and Chazy, which 

 Ells placed in the upper part of division B but found obscure, may thus possibly 

 lie at a higher horizon. 



Logan's section of divisions C and D runs as follows, from the base upward : 



[Divi3ion] 0. 



Feet. 



1. Black and dark-gray compact limestones, weathering lead-gray, witli a few bands of dove- 



gray. The beds are all massive and afford abundance of a few species of Testacese, the 

 whole of which appear to have the peculiarities of being large sized and thick shelled and 

 occurring in numerous isolated patches, which vary in diameter from about 3 to 10 feet. 

 The fossils are several undescribed species of Murchisonia and Pleurotomaria, Ecculiom- 

 phalus canadensis, E. intortus, E. spiralis, several undescribed species of Ophileta, Maclurea 

 ponderosa, several undescribed species of Orthoceras, and one of Nautilus. Toward the 

 base Maclurea ponderosa seems tabe somewhat smaller than in theupper part of the deposit, 

 and toward the top one or two beds appear to be of a partially conglomerate character ... 150 



2. Black slates, or posiibly thin-bedded black limestones, with a few thicker beds toward the 



top ; the mass is altogether very imperfectly seen 170 



320. 

 [Division] D. 



1. Black limestone conglomerates, composed chiefly of the ruins of the thick-bedded lime- 



stones of division C. The inclosed masses vary in size from pieces of an inch in diameter 

 to blocks containing 50 and 60 cubic feet and are cemented together by a calcareo-magne- 

 sian paste. Of this, however, from the closeness with which the masses are packed together, 

 there is but a very small quantity. The limestones are generally close grained and black 

 or dark gray in color, but there are mingled with them a few scattered blocks of a light- 

 colored yellow-weathering dolomite, some of them a foot in diameter. Many of the masses 

 of limestone contain fossils, and the species are almost wholly confined to those aheady 

 stated as characterizing the parent beds C 1. There appear to be at least two principal 

 bands of this conglomerate, 'each varying in thickness in different parts from about 50 to 

 100 feet. There is an interval'ibetween them of from 100 to 150 feet, occupied by black 

 slates holding rounded masses of limestone, which convert parts of the mass, varying in 

 thickness from 10 to 20 feet, into slaty conglomerates. In some parts either the interval 

 between the main two bands of conglomerate increases considerably or there is a third 

 band with similar slates, intervening between it and the second. The whole is con- 

 tained in a thickness of from 250 to 300 



2. Black and greenish argillaceous slates, probably iiiterstratified with occasional thin calcare- 



ous bands and thin lenticular patches of limestone conglomerate, as well as more important 

 bands of yellow-weatheHng dolomitic slates. The whole is terminated by a band of black 

 limestone conglomerate similar in character and thickness (from 50 to 100 feet) to those 

 already mentioned and containing Maclurea ponderosa in one of the few places in which the 

 band has been seen. This whole mass of strata is very imperfectly exposed, and much 

 uncertainty exists as to its true general character. Its thickness may be from 750 to 1,000 



3. Gray and black striped slates, some parts of which are calcareous and weather slightly 



brownish. They are interstratified with occasional thin beds of black limestone, weather- 

 ing lead-gray, as well as many strong and solid beds of brown-weathering magnesian lime- 

 stone and brown-weathering dolomitic slates. Some of the latter are marked by an 

 abundance of fucoids resembling Buthotrephis flexuosa of Emmons. Occasional beds of 

 sandstone, from 1 to 3 feet in thickness, are met with. About the middle of the mass 

 there has in one place been observed a bed of limestone conglomerate from 5 to 10 feet thick, 

 and other similar ones may occur in different parts of the vertical thickness 1,500 



2,800 



In commenting on this section E. 0. Uh-ich states that division C is probably 

 Beekmantown and division D suggests the Rysedorph conglomerate of the New 

 York State Survey reports, although D 1 is probably older. 



