36 



becomes at once apparent that the most fossiliferous beds 

 are those near the top of the series, namely the Demissa and 

 Stictopora beds. As the water became purer towards the 

 close of the deposition of the Hamilton shales, the braehio- 

 pods, which occurred sparingly during the greater part of 

 the time, underwent a luxuriant development, all the im- 

 portant and characteristic species growing in great pro- 

 fusion. The change of conditions, however, which succeeded, 

 drove out most of them, and when the water became pure 

 enough for the growth of the limestone-building corals and 

 crinoids, a quite distinct assemblage of species appeared. 

 (See further, Chapter III.). 



In the lower beds the fossils are scattered, from some, 

 thev appear to be entirely absent. Down to about 

 three feet below the Encrinal limestone, the shale contains 

 species such as are found in greater abundance in the Demissa 

 bed. Associated with these is Athyris spiriferoides (Eaton), 

 which here reached its last abundant development. Below 

 this, down to about four feet below the Encrinal limestone, 

 fossils are very rare, with the exception of the two species of 

 minute needle-like pteropods, Stvliolina fissurella (Hall) and 

 Tentaculites gracilistriatus Hall, both of which occur in 

 vast numbers on some of the shale laminae. With them 

 occur several species of minute ostracod crustaceans, among 

 which the Primitiopsis punctulifera (Hall) predominates. 



Still descending, we find the fossils somewhat more 

 abundant, but in no case do they approach the numerical 

 development found in the Demissa bed. The only constant 

 and abundant species throughout these shales is the type 

 species of the fauna, the broad-winged Spirifcr mucronatus 

 (Conrad ). 



Nine feet below the Encrinal limestone, or at the base of 

 the section at its lower end, and forming a portion of the 

 stream bed, is a layer of large, flat calcareous concretions, 

 occasionally united into a continuous bed ; but chiefly com- 

 posed of separate masses. These contain a large number of 



