31 



The thickness of the stratum is one and one-half feet, vary- 

 ing but httle in different parts of the section. Its upper 

 portion is of a somewhat shal y character, and highly fossili- 

 ferous. More than fifty species of fossils have been obtained 

 from this portion of the stratum, man^^ of them being either 

 rare or unrepresented outside of it. One of the most 

 striking species is a large pelecypod, which is found in con- 

 siderable numbers in the upper part of the limestone, near 

 the lower end of the section. This is the Mytilarca oviforniis 

 (Conrad ), a large mussel shell w^hich is not found outside of 

 this bed. The shell is commonly removed, the "mould" of 

 the interior alone remaining. The rock is composed chief!}'- 

 of the finely comminuted remains of calcareous organisms, 

 among which crinoid stems and joints predominate. 

 Weathering brings the coarser of these out in relief, a 

 character often observable on the moulds of such shells as 

 the Mytilarca. 



Although fossils are numerous, perfect specimens are diffi- 

 cult to obtain. This is due to the fact that the outer la^^er 

 of the shells tends to adhere to the rock on being split 

 out. This exfoliation is not restricted to shells alone, 

 but occurs in the trilobites and other organisms as well. It 

 is only where w^eathering has removed the surrounding 

 matrix that the perfect surface characters become visible. 

 The lower, more solid and more cr\'stalline portion of the 

 bed contains chiefly corals, among which the hone^'comb 

 coral — Favosites hamiltonix (Hall) predominates. It 

 usually forms rounded heads six inches to a foot in diame- 

 ter, sometimes containing petroleum, probably the result of 

 the decomposition of the original animal matter. 



The rock is pyritiferous in places, sometimes so to a con- 

 siderable degree. On its under side occurs a coating of iron 

 sulphide, probabW in the form of the mineral marcasite, 

 which occasionally has a thickness of an inch. From the 

 oxidation of this mineral, the rock is stained a reddish 

 brown color. This feature diminishes the value of the rock 



