OOKKI I TKATA. v. \ 



feet The rocks contain considerable chert and the fossils are nearly always silicifled. 

 Characteristic fossils are Teiradiinn columnar*, <'l<uiuirin hulli, < '. carterenai*. Slri-i>ti-ln*ma 

 prof HIK I n in. h'ni'huifiHiiinn &i/>i'ri'(/<i. Slrmii<itt>i-i-riHin ruyosum, Triptocerat pUinodortalutu, 

 Ai-tinocrnu bigibyi.Orthoceraiarciuiliriilniii. O.lfmn-uri, T. }>ltinoconvfrvm,Orthi prclineUu, 

 RfCfpfaculiles occidentala, and Cnmnriiclmliii rugosa (Ulrich).* 



In Wisconsin and Illinois the group is represented by the "Upper Buff" and "Upper 

 Blue limestones." The average thickness of the two beds here is probably less than 40 

 feet They are well exposed in the quarries at Rockton. Illinois, where the upper member 

 carries fossils clearly indicating the Phylloporina and Fucoid beds of the Minnesota 

 section. We collected here, namely, Orthu pectinella, O. intfuilimiritt, Slrophomena 

 trrnlonensis, Agelacrinus maryintilitt, Hythotrypa laxaia, Rqflnesquina inquassa, Arthropora 

 f>i/nrr<i/a, Pratoporn oonoidca and Byihopora alcicornis. In the Upper Buff, which we 

 correlate with the Rhinidictya and Ctenodonta beds of Minnesota, we saw Sirepieluama 

 profundum, Pocky did y a occiiii-nlitlig. Phylloporina rrlicututii, Rhinitlictyd mulaliilis, 

 Cyriodonla cingulata, Vanuxemia niota and Cyrioceras eorniculinn. Numerous other 

 Cephalopoda occur in this bed but they have not been identified in Minnesota. At Beloit 

 and other localities in Wisconsin the Upper Buff contains some chert 



The strata representing the Black River group in Minnesota are peculiar in consisting 

 almost entirely of shales. They are also more fossiliferoas than elsewhere, and the fauna 

 taken as a whole is unusual in two respects. Namely, it includes a large number of 

 Bryosoa which are wanting entirely in other regions, while the Cephalopoda, for which 

 the group is noted, are here represented by relatively small species only. Another 

 remarkable feature is the rapid reduction in volume between Cannon Falls and localities 

 in Fillmore county. (See sections 6, 7 and 8). This is so marked that we are almost 

 justified in assuming that the entire group failed a few miles east of Fountain. Unfortu- 

 nately, this cannot be proved since the strata of the Trenton period have all been removed 

 in that direction. While the Stones River group may still have continued without material 

 interruption across the Mississippi valley, at the southern end of the state, the Black River 

 group probably did not do so, and we are inclined to believe that the latter, as well as 

 the succeeding Silurian and Devonian strata of southern Minnesota and northern Iowa, 

 were deposited in a bay. 



The la*t of th<Me foe*lb I* the lance fucold " that I* to extren.Hy abundant and <-l.arartrri.tlo of Ue faootd tod 

 In Minnesota- la Meroer county, Kentucky. It occura at an exactly equivalent burUoo. <. .. In a thin bed of abale near Ik* 

 u>p of the Black Hirer llnmtone. The fomll weal to <u to be a cut of a branching ipooe lllar to the Plain ilttlt 

 tlchotoma described by Ulrich and Everett from the ponce layer of the Stone* River croup at HI ton. Illlnoto. C. rapm I* a 

 much lanter upeclea. IU flexuotu oonpremed braacbe* rarylnc from 5 to over IJ mm. In width. The bifurcation, vary 

 crcatly. belac omeUrne* very cloee, at other ttmea far apart. A a rule the peelmetti ahow little itruoture. appearinc a* 

 ere Moay flattened branch** with mote or lev obeeure traaivenw and oblique furrown. The mail complete pedtnea* are 

 covered with an Irrecnlar network compoaed of coane noduloee thread* often exhlbltlnc a loocltudlnal arraDcement. 

 illy the network remain* on one *lde of the brancbe* only. When removed entirely the ctemi are Men to be oompoeed 

 r i.o eleaenU: <1) a .Ipbuaole-llke, *ubeyllndrical r.l. with annulatkiM and ooutrtcUone 1 lot mm. apart, and fTi a 

 erlea of oblique wpta-llke partlttoot-eeoer.lly two u> each *nnulatl..n-<-laaplnc the annulawd rod *o a* to leave about 

 ooe-iblnl of It* circumference expoeed to view. Not Infrequently the rod , l.ancee suddenly from oor .Ide of the branch to 

 the other. Inaa unbraached framee>t before u* UU occur* twice In thecpaecof mm. The beet *peele*j* were fovad 

 Dty. 



