THE LOWER SILURIAN ROCKS. 561 



I. 



Carbonate of lime 84.02 



Carbonate of magnesia ... 5.33 



Silica 7.03 



Alumina 2 . 21 



Iron sesquioxide 83 



Iron protoxide 39 



Water .61 



100.42 99.87 100.62 



The following list of fossils includes all that I have observed in 

 the Trenton beds. The determinations are mostly by Mr. E. P. Whit- 

 field: 



Name. Horizon at which found. 



Petrctia (Streptelasma) corniculum, - Occurs throughout the 



Buff but most com- 

 mon in the lower part. 



Columnaria alveolata, ....... Lower part of Buff. 



Graptolitic markings, ------ Lower part of Blue. 



Crinoidal columns, ...... Upper part of Buff. 



Otihis tricenaria, ------- Buff. 



Streptorhynchus filitextus ..... Buff. 



S. deflectus - Buff. 



Strophomena camerata, ...... Buff. 



S. incrassata, - - - - - Buff. 



Rhynchonella, n. sp., ...... Buff. 



R. n. sp., Blue. 



Tellinomya cuneata, ------- Buff. 



CypricarditeS ventricosus ----- Buff. 



Raphistoma lenticulare ------ Buff. 



R. Nasoni, ....... Buff. 



Trochonema umbilicatum ----- Buff. 



Murchisonia bicincta, ------ Buff. 



M. tricarinata, ------- Buff. 



Pleurotomaria subconica, Buff, 



Helicotoma planulata, ...... Buff. 



Orthoceras annulum, ------ Buff. 



0. vertebrale, ....... Buff. 



Gyroceras duplicostatunb n. sp., - Buff. 



Oncoceras pandion, ------- Buff. 



Cyrtoceras, mid. sp., - - - - - - Buff. 



Beside these, obscure and fragmentory casts of Orthoceratites are 

 very numerous indeed in the Buff, varying greatly in size, some 

 occurring as great as 6 feet in length and 8 inches in diameter. The 

 fossils of the Buff are almost wholly in the state of casts of the in- 

 terior, or impressions of the exterior. Of those in the list, the most 

 frequently met with are the coral Petram, and the gasteropods, 

 amongst which Trochonema urnbilicata is the most abundant. These 

 Wis. SUR.--36 



