GEOLOGICAL SEQUENCE OF THE DOWNING BEDS. 29") 



being perhaps twenty-five, Ostracods by several species of 

 Unto mis, and Polyzoa by Fenestelia, Glauconome, &c. It is worthy 

 of note that in this bed also occurs FJiillipsastrea Verneidll, which 

 in Britain is a Devonian fossil. Sponges are represented by 

 six-rayed spicules. 



In the Middle Trilobite or Phacops bed, corals have dwindled 

 down to a few genera of which the most prominent is probably a 

 Zitphrentis. Crinoids are represented by stems, Brachiopoda 

 chiefly by Orthis and Leptoma. One of the former is probably 

 0. testiidiaaria. Gasteropoda by Etioniphalus, and P/eurotoinaria. 

 Pteropoda by Conularia. Cephalopods by Orthoceras. The in- 

 dividuals belonging to any of these genera except Orilus and 

 Leptcena, are poorly represented. Here, as in the previous bed, 

 trilobites are the most characteristic feature. They are represented 

 by live or six genera as follows : — Phacwps, including probably P. 

 cau<latus, P. lonyicaudatus and P. fecundas, Acidaspis three or 

 four species, A. louyisinnns and A. Leonhardi being among them. 

 Proetus boiotiiugensis, and Cyphaspis. The individuals belonging 

 to the species of most of these ^fenera were numerous ; but those 

 of P. caudatus and P. longicandatits were particularly so, and their 

 remains form a large proportion of the rock constituting the bed. 



Of the life in the Great Shale bed there is little to record. 

 During the period taken for its formation many of the forms of 

 life found in the preceding beds apparently became extinct and 

 some new forms made their appearance. In the Upper Trilobite 

 bed, the Brachiopods are represented by Leptmna ; Gasteropoda 

 by Jfarchisonia, Loxonema, Eiwiaphalas, Belleruphon and others. 

 Lainellibranchs by several genera, making an approach to the 

 Devonian. Pteropods by Conidaria. Cephalopods by Orthoceras. 

 Trilobites are represented by Acidaftpis longispinus and A. Leon- 

 hardi, Phacops caiulafAis and P. fecund/is ?, Proetus, Cyphasjns 

 Boivningensis, and Calyineiie BhtmenbacJdi. 



The corals number two or three genei'a only, the most important 

 being Pleurodictyutn. 



The general facies of this bed shows a rapid approach to the 

 Devonian Group. The Brachiopods exhibit a great diininution 

 both in genera and species, and on the other hand the Lamel- 

 libranchs have increased, a further evidence of the transition 

 above referred to. 



In the Upper Conglomerate bed, I have found corals repre- 

 senting a good many genera belonging to the limestone beds 

 below, and some Orthis, RltynrJionella, and Megalodoii. 



In addition to the fossil above enumerated, I have obtained 

 several graptolites from micaceous sandstones in the Lower 

 Trilobite bed, on the eastern side of the syncline ; and in shaly 

 sandstones on the western side, in the Great Shale bed. 



