LOWER HELDERBERG LIMESTONE. 393 



The remains of Leperditia, found at this locality, are very abund- 

 ant, literally covering the surface of some layers, and, to a greater or 

 less extent, disseminated through the mass of some of the beds, but 

 unfortunately the state of preservation is poor. A careful examina- 

 tion and comparison of a large number of specimens leaves no doubt 

 that the fossil is Leperditia alta, or a very closely related species. 



In the bed of the river a little above this locality, very thin beds of 

 a softer, dark dolomite, colored by carbonaceous matter, are found. 

 Some of the layers are marked by numerous black or dark brown car- 

 bonaceous laminae, which give to the rock an appearance quite pecu- 

 liar. This carbonaceous matter is evidently derived from the remains 

 of plants, many indications of which are present, among them forms 

 resembling Sphenothallus. In addition to these, two species of 

 Orthis are found, one resembling Orthis oblata, and the other closely 

 similar to Orthis subearinata, but smaller. Pterinea aviculoidea, or 

 a very closely allied, if not absolutely identical, species, an imperfect 

 Orthoceras, and a doubtful Inocaulis, are also present. 



Farther up the stream, on the opposite side, a quarry has been, 

 opened which exhibits a more compact, close textured rock, and one 

 intermediate in lithological character between these and the Niagara 

 limestone. No fossils were found in it, and its relationship is uncer- 

 tain. Its most striking peculiarity is the strong undulation of its 

 strata, which allies it rather with the Niagara than with the forma- 

 tion under consideracion, whose beds have never been observed other- 

 wise than as horizontal and perfectly plane. 



The composition of the formation at this point is shown in the 

 following table of analyses by Mr. Bode; No. I being the rock asso- 

 ciated with Leperditia; No. II being that in which the cavities filled 

 with spar occur; and No. Ill being the dark fossiliferous rock from 

 the river bed: 



I. II. III. 



Carbonate of lime 53.233 56.552 52.786 



Carbonate of magnesia 41 .573 41 .504 43.781 



Silica 2-905 1.287 3.094 



Alumina 1-462 0-168 0.097 



Oxideofiron 0.827 0.495 0.242 



Total 100.000 100.006 100.000 



It will be observed that they are all essentially dolomites, with a small 

 percentage of impurity, and that in composition they do not essen- 

 tially differ from the Mud creek rock. 



The location of this peculiar deposit adds interest to the problem 

 of its age and relationship. A little more than two miles to the 



