29-4 GEOLOGY OF EASTERN WISCONSIN. 



The following is a partial list of the species that lived during the 

 deposition of these strata: 



Buthotrephis succulens, Streptelasma (Petraia) corniculum, a new 

 species of Stictopora and one of Trematopora, a Lingula, resembling 

 L. obtusa, Orthis disparalis, O.perveta, 0. subquadrata, O. tricenaria, 

 Streptorhynchus deflectum, S.filitextum, 8. dettoideum, /S. planum- 

 lonum, Strophomena alternata, S. camerata, S. camura, S. incras- 

 sata, a new species of Hhynchonella, Tellinom.ya nasuta, Cypricar- 

 dites Canadensis, C. rectirostris, C. -rotundatus, C. subtruncatus, 

 C. ventricosus, C., n. sp., Modiolopsis superba, Ilelicotoma planu- 

 lata, Raphistoma lenticularis, R. Nasoni, Pleurotomaria subconica, 

 Trochonema arribiguum, T. umbilicatum, Murchisonia tricar india, 

 M. bicincta, Subulites elongatus, Bucania bidorsata, Bellerophon 

 bilobatus, Pterotheca attenuata, Orthoceras anellum, O.junceum, O. 

 vertebrale, O., n. sp., 0. Beloitense, Oncoceras Pandion, 0. plebeium, 

 Gyroceras convolvans, Lituites occidentalis, Illcenus taurus, Cer- 

 aurus pleurexanthenws and Leperditiafabulites. 



It is impossible in the present state of our knowledge to name any 

 single fossil of common occurrence that is peculiarly characteristic 

 of this geological horizon The abundance of Lamellibranchiates, 

 Gasteropods and Cephalopods, and the fewness of the Corals and Bry- 

 ozoans sufficiently distinguish it from both of the Blue beds above, 

 but not from the Upper Buff beds to which this division bears a strong 

 resemblance paleontologically as well as lithologically. At some 

 points the Lower Buff beds develop something of a shaly character at 

 the base, and are highly fossiliferous, in which cases the facies of the 

 fauna strongly resembles that of the Blue beds, which are likewise 

 shaly. It appears from all the facts that there was an alternation of 

 conditions in the depositing Trenton seas, and that when the condi- 

 tions were such as to favor the formation of limestone simply, the life 

 above characterized predominated, and that whenever the conditions 

 changed so as to cause a deposit of shale interleaved with layers of 

 limestone, the brachiopodous and coralline fauna prevailed. These 

 subdivisions then signify rather physical mutations of a more or less 

 local nature, than wide spread changes in the life -character of the period. 



2. The Lower Blue Beds. The upper surface of the preceding di- 

 vision is at most points well defined, and upon its thick beds rest an 

 alternating series of thin, impure limestone layers and thinner shaly 

 leaves. These are usually grouped into more massive beds, and where 

 removed from the action of surface agencies, the shaly portions often 

 possess sufficient coherence to bind the limestone layers into beds of 

 respectable dimensions. 



