﻿3i Range of Trenton Species 13 



Remarks. 



The measurements give the same total, 270 feet, obtained by 

 Prosser and Cumings.* 



It is interesting to note the relative abundance of each of the 

 prominent species through the various zones. 



Dalmanella teshidinaria. — Rare in A and B, it becomes com- 

 mon in C and D, rare again in E and F, then common all through 

 the rest of the section, its greatest abundance being in K and L, 

 which might be called the Dalmanella zone were it not that it 

 remains abundant to the top. 



Pledambonites sericeus. — Very rare at the base, it becomes 

 very abundant in D, 35 feet above. From E to K it is again 

 rare, then becomes more common and finally abundant in M, 150 

 feet above the first Pledambonites zone. It remains fairly common 

 to the top. 



Rafinesquina alternata. — Common at the base, it becomes rare 

 • for a short distance and then fairly common throughout the 

 greater part of the section. 



Rafinesqiiina deltoidea. — This fossil does not appear until the 

 top of K is reached, 130 feet above the base, and then it is rare 

 until it suddenly becomes very abundant in N at 200 feet. In 

 the later zones it is again less common. 



Platystrophia lynx. — Absent from the lower 35 feet, then occurs 

 very rarely up to K, when it becomes abundant in L at 175 feet, 

 rare in M, common in N, and abundant again in O and P, making 

 two zones about 50 feet apart. 



Tripletia extans. — Found only in the first 15 feet and in J. 



Trematis terminalis. — Found rarely all through the section, and 

 is common only in G. 



Bellerophon bilobatus. — In all horizons but is more common 

 above the 70 foot level, reaching its culmination in the Bellerophon 

 zone at 160 feet. Above that point it is rare. 



Asaphus platycephalus. — This trilobite is more common in the 

 lower layers, reaching a maximum in E, only 50 feet above the 

 base. It continues through the remainder of the rock. 



Calymene se?iarla. — About the same history as the preceding. 

 It is most common in the trilobite zone, but may be found in 



*Prof. C. S. Prosser gives 275 ft. as the result of a later measurement. 



