LOWER TRENTON FOSSIL BEDS. 



606 



Lepta nit si ricea, Sowerby. 



Orthis bellarugosa, < lonrad. 



0. subsequata, Conrad. 



0. testudinaria, Dalman (variety). 



0. tricenaria, Conrad. 



Rhynchonella ainsliei, N. H. Win- 



chell. 

 R. minnesotensis, Sardeson. 

 Streptorhynchus filitextum, Hall. 

 Strophomena alternata (/), Conrad. 

 S. halli, Sardeson. 

 S. inquassa, Sardeson. 



P. mbconica, Hall. 

 Raphistoma lenticulare, Emmons. 

 Subulites elongatus, Emmons. 

 Trochonema umbilicatum, Hall. 

 Cypricardites subtruncatus, Hall. 

 C. ventricosus, Hall. 

 Modiolopsis plana, Hall. 

 M. superba, Hall. 

 M.faba, Emmons. 

 Tellinomya levata, Hall. 

 T. ventricosa, Hall. 

 Whitella compressa, Ulrich. 



The Fucoid Bed. — This is 20 feet thick, consisting chiefly of very argil- 

 laceous material so abounding in fucoidal remains that the name Fucoid 

 is given. It differs from the underlying Stictopora bed in being full of 

 calcareous and siliceous laminae, besides masses of sponges, Raufella fili- 

 osa and R. palmipes, and various bryozoa. There are also thin layers of 

 limestone from one to six inches thick, of which one is markedly oolitic 

 and limonitic. In these respects this layer reminds one of the oolitic top 

 of the upper magnesian layer, Shakopee A. This oolitic-limonitic layer 

 has been recognized in Ramsey, Goodhue and Fillmore counties. The 

 uppermost strata are of firm crystalline limestone, 3 feet in thickness at 

 Saint Paul. It may prove to be less firm in the Southern area of the 

 formation. 



The fossils are as follows : 



Phylloporina corticosa, Ulrich. 

 Prasopora contigua, Ulrich. 

 P. conoidea, Ulrich. 

 Pachydictya occidentalism Ulrich. 

 Stictopora mutabilis, Ulrich. 

 ('run in setigera, Hall. 

 Leptssna sericea, Sowerby. 

 Orthis minnesotensis, Sardeson. 

 0. pectinella, Emmons. 

 0. subssquata, ( lonrad. 



0. rogata, Sardeson. 

 0. trici naria, Conrad. 

 Rhynchonella increbescens, Hall. 

 Streptorhynchus filitextum, Hall. 

 Strophomena alternata, Conrad. 

 S. minnesotensis (/), N. H. Winch ell. 

 Zygospira recurvirostris, Hall. 

 Mufchisonia milleri, Hall. 

 Pleurotomaria subconica, Hall. 

 Subulites elongatus, Emmons. 



The Zygospira Bed. — A layers fret thick from the top of the Fucoid 

 bed upward has been separated mainly on paleontologic grounds ; yet it 

 may be distinguished from the Fucoid bed by the presence within it of 

 numerous rounded calcareous masses rather than calcareous laminse 

 such as those of superior member. 



XI. IX Bun. Gkol. Soc. Am., Vol. 3, 18U1. 



