DISCUSSION AND CORRELATION 161 



A, where, as nearly as can be ascertained from the overgrown character of 

 the exposure, it has a thickness of about 4 feet. This Spirifer is by no 

 means confined to this bed, for it is abundant in the coral layer at Section 



B, and at Bartlett's mills, though it is not always possible to decide what 

 proportion of individuals may have come from the weathered beds just 

 above, where this variety is not uncommon. 



The highest bed (number 5) exposed at Bartlett's mills represents only 

 the lower part of bed 5 of the Rock Glen section, while bed 4 is found in 

 both localities, retaining its lithic and physiographic features. 



In the Rock Glen section, about 6 feet above the bed where Spirifer 

 mucronatus var. thedfordensis is abundant, the calcareous beds with Cera- 

 topora begin. In the Thedford section (Section A) the interval between 

 the Spirifer beds and the calcareous Ceratopora beds is about the same, 

 though from the unsatisfactory character of the section precise measure- 

 ment was not possible. There can be little doubt, however, that the 

 upper calcareous, beds of Section A and those of Section D are equiva- 

 lent, and they have been numbered accordingly in the sections. 



Beds number 7 and 8, which are recorded with a combined thickness 

 of 10 feet at Section A, are at Section D divided into 8 feet of shale and 

 18 inches of argillaceous limestone. Only about 10 feet of bed 6 are ex- 

 posed at Section A, while its thickness in Rock glen is 18 feet. 



It thus appears that the section near Thedford station (A) represents 

 the upper part of the Rock Glen section, stopping in the lower part of bed 

 6. At Section B the succession is carried downward through the En- 

 crinal limestone. The characters of this latter rock are not well exhibited 

 at Section B, but at Sections C, D, and E — the Brickyard, Rock glen, and 

 Bartletts mills respectively — it is well shown. In each of these expos- 

 ures there is a bed of fissile bituminous shale intercalated in the lower 

 part of the limestone. At the Brickyard this bed is from 2 to 4 inches 

 thick ; at Rock glen it is 3 inches thick, while at Bartlett's mills it ranges 

 up to 6 inches in thickness. This bed is generally filled with crushed 

 specimens of Leiorhynchus. 



Among the characteristic fossils of the Encrinal limestone are Spirifer 

 (Delthyris) sculptilis, Favosites turbinata, and Craspedophyllum archiaci. 

 Of these Spirifer sculptilis has not been found by us outside of the Encrinal 

 limestone. Tropidoleptus carinatus is also represented by a single speci- 

 men from the Encrinal limestone in our collections. Spirifer divaricata 

 was likewise found by us only in the Encrinal limestone ; Rhipidomella 

 penelope and R. vanuxemi also occur here. 



The lower Hamilton shales (bed 1) are exposed at the Brickyard, Rock 

 glen, and Bartlett's mills — Sections C, D, and E respectively. At the 

 Brickyard 15 feet are exposed ; at Rock glen from 21 to 25 feet, while 



