410 R. M. Field — Middle Ordovician of Central 



discussion of each formation in order. The numbers in 

 the left hand column refer only to the thicknesses of 

 the formations in the Belief onte section. All of the solid 

 black bars below the Valentine designate Tetradium 

 beds, and the Rodman is also shown by a solid black bar. 

 The solid black bar at the base of the Coburn indicates 

 the Parastrophia zone. Particular horizons are marked 

 by letters, the Stones River series being A 1 , B 1 , C 1 , etc., 

 the Trenton series A 2 , B 2 , etc. Intraformational struc- 

 tures are shown by the pattern as illustrated in B 1 . 



Loysburg Formation. — The dark and impure, dolo- 

 mitic limestone which lies between the Beekmantown and 

 the first intraformational zone has been named Loysburg, 

 after the town by that name in the northern part of Bed- 

 ford county. Collie does not appear to have recognized 

 the existence of this formation, for in his description of 

 the section at Belief onte he makes no distinction between 

 the lithology and faunal characteristics of the lower and 

 upper Stones River. Butts also does not mention the 

 lowest division of the Stones River group, probably be- 

 cause it is poorly exposed in the section at Roaring 

 Spring. The Loysburg differs from the superjacent 

 Carlim not only in lithology and paucity of fossils but 

 also in the total absence of the reef -building organisms 

 so characteristic of the latter formation. Only the 

 upper 115 feet are exposed at Bellefonte and the base 

 can not be located with any degree of accuracy. The 

 only other section in which it is well exposed is at Loys- 

 burg, where it appears to be somewhat less thick. 



Carlim Formation. — The contact between the Loys- 

 burg and the Carlim is well exposed in the Section at 

 Loysburg, where the line appears to be quite sharp 

 between the dark, impure and the light-colored purer 

 limestone. There is no evidence of an interformational 

 conglomerate at the base of the Carlim, but wherever the 

 base of this has been observed it is characterized by 

 strongly marked intraformational structures, which at 

 first sight suggest a fine-textured basal conglomerate. 

 These structures are the most striking characteristics of 

 the Stones River group and the writer has been able to 

 trace them from New York to Tennessee. It is obvious 

 that the elucidation of these phenomena is intimately 

 connected with the study of disconformities and no dis- 

 cussion of the correlation of the lower Middle Ordovi- 



