CORRELATION OF STRATA. llXXvii 



2. Twelve feet of shelly or thin-bedded argillaceous limestone, tbo surface of the layer*. In the 

 I..W.T half especially, being rmitfh v . I'M- middle several large Impressions of Btotptaeutite* owrni, <.. 

 Hilt.- ilf!.-.-n I iii-he.. in <llani.-i,-r. were noticed. Fossils ire neither very plentiful n..r well preserved In 

 these lav. 



3 Twenty-nine foet of rather thin-bedded, compact, bluish-gray, limestone, the purity of the 

 limestone Increasing from below upward. Contains nunterous foMlllferoun layer*, the foMll* being chiefly 

 Brachlopoda of the far-illy ^ropHamtMa, Of other forms a flne new species of Potoocrfniu deserve* 



Iliellliiill. 



4. Nine feet of cherty limestone. Fossils abundant, Orthi* trieenoria, O. plicaieUa, Strophomena 

 btilinyri, riihimbnnitu ditertiu, PartufropUa hfmiplieata, and some branching niontlcullporolds. 



5. Flfty-sli feet of One-grained and subcrybtalllne limestones; some argillaceous layers, thinner 

 than u-u:il. in the upper twelve feet About eleven feet beneath the top we flnd a layer full of graptolltes, 

 probably >f th.- p-mis i>ipl-ir,>i>tut. Above this layer fossils are comparatively rare, but beneath It they 

 are al.'iii.l:iMt though r jt h-r illrtlcutt to obtain perfect, since they must be broken out of the solid lime- 



\ . r . ,.TS we obtained here Rafnetquina deltoidea, PledamboniU* gibbon, Zyyotpira upVimi, 

 Anbmyekia belK#riata, ByuongfMa inltrmtdia, CWonyeWa undnta, CUnodonta intermedia, Cjrrtodon/n abrupta, 

 C. gtrmana, E*dode*m tuneatwn, X. camprtMum, PiUoconrhaf minruvXennt, EcryliopUnu ouxmanu* 

 JNuwptra inflala, F. nobilu. F. pl'inulata, Tmchonema roWnwi and I'latgmetoput robbinti. 



At-.ve No. S this ravine exposes about Ofty feet of massive dolomltlc limestones of the Maclurea 

 bed and then about twenty feet of shaly layers belonging to the Utlca group. 



Sections, Moving ttrnta at MMI in ond near a tmaU quarry, about too and a half mUa north of Spring 

 Valley, Minnetota. 



1. About nine feet of thin and unevenly bedded or laminated, bluish-gray, crlnuldal limestone. 

 The whole appears solid in a fresh exposure but breaks up under the weather. The crlnoldal fragments 

 have evidently been much rolled. 



2. Twenty feet of even bedded, compact, gray limestone. In layers fifteen Inches or leas thick, 

 i.vers becoming too thin and argillaceous In the upper part for building purposes. Between the lime- 

 stones there are bands of soft shale, the whole bed being composed of about one-third shale and two- 

 thirds limestone. At the top several layer* will be noticed containing the separated parts of Amphut or 

 Itatelut mnximu* In abundance. Six feet beneath the top a band of shale contains Leptobolta oondcn/<itu. 

 three speclos of Lingula and Climamgraptu* typicalit (f). Beneath this there Is another band from which 

 Ortkit (Mtuifiu'iri.i, varieties multuetta and emarfratn, and two dlscoldal species of Bryozoa were obtained 

 In considerable abundance. The same layer afforded also Tripleeia ulriehi, Pledambonitu praecotii (Sarde. 

 *on) and CnlymeM callictphala var. mammi7/irn. 



3. These are covered at this locality. About a mile east of Spring Valley they are exposed as 

 thin bedded, arenaceous and argillaceous limestones; some of the layers are full of Hrachlopoda and other 

 fossils characterizing the Richmond group of the Cincinnati region. 



4. Arenaceous strata, six feet thick, weathering Into Irregular lumps, some of which contain 

 plates and columns of large crlnolds or cystideans. and Hindia *phatrodali. Probably Upper Silurian. 



5. Four feet of rather coarse sandstone. Including here and there an abundant supply of small 

 quartz pebble*. 



0. Above No. 5 the surface of the ground was strewn with Irregular, porous lump* of yellow 

 or bnff, magneslan limestone of Devonian age. 



CORRELATION OF STRATA. 



TRENTON PERIOD. 



Chaay group. 



St. Peter Sandttont. A number of fossils have been found in this well known division 

 of the Lower Silurian, but they are nearly all very ill preserved, the nature of the sediment 

 being unfavorable. As they have not been included in this report, it may be well to say 

 of them that, as far as their condition will admit of judgment, they are of types reminding 

 one as much, perhaps, of species characterizing the Stones River group as of Chazy 

 forms. It is. however, as a part of the latter group that the St Peter is to be viewed. 



