CORRELATION f>l -Ti:ATA <-\ 



bed becomes thicker and more argillaceous, taking it as a whole, and contains molluscan 

 species of the genera < 7-i.;'/.ii/.i, < 7,./,.;i/,,.r/is and Orlhooertu in increasing abundance. 



u' upon the Utica we find in Fillmore county from 10 to perhaps 25 feet of more 

 or less thin bedded argillaceous and siliceous limestones belonging to the Richmond ;rroup. 

 Some of the layers are full of tin fossils, chiefly Brachiopoda. and these are often silicifled, 

 in which condition they have been collected by hundreds near Spring Valley. With very 

 few exceptions, all the fossils that have been found in these layers occur also in tin- 

 'imond group <>f Illinois. Indiana and Ohio 



The strata of this group in Fillmore county are quickly decomposed and covered with 

 soil, so that satisfactory natural exposures are rare. The fossils may sometimes be picked 

 f the worn soil of old fields but a more abundant supply was obtained in the cuttings 

 along the railroad between Wykoff and Spring Valley. A few of the characteristic species 

 ii-tliin snl><in<i<lr<il<i. a. /n-'Mii-il,!. i> 'futmliiutrin (large variety). O. tchitfu-lili, l\nfinfquinn 

 Whitfield sp., Rhynclmnrlln m/xtr. Xlrophomena neglt'ctn, /.'<i/>/o;/iu rarinhili; Ctcm> 

 lunln ximilin. ('. n-i-nrrn and .SYrv/jMaamn nixticiim. 



lying the fossiliferous layers of the Richmond group, may be Keen in two places 

 near Spring Valley, one about two and one-half miles north, the other one mile east of 

 the town, about six feet of sandy layers weathering into irregular lumps and thin shells. 

 Some of these contained fragments of large crinoidsor cystids, and from the loose material 

 we obtained several fine examples of Hm-lin sphceroidulit, a common Upper Silurian 

 foisil; also spiculesof Ifyalonit-Hn suliwytt which occurs nearly everywhere in connection 

 with tin- IHntliti. Though these six feet are probably to be regarded as Upper Silurian 

 the passage lithologically from the Richmond group is exceedingly gradual. 



Succeeding the foregoing bed and followed with not very strong evidences of uncon- 

 formity by Devonian strata, is a sandstone four feet thick which here and there contains 

 large numbers of small quartz pebbles, varying between one and ten mm. in diameter 

 This sandstone we assume to belong to the Oriskany of New York. 



TABULATION OK THE LOWER SILURIAN SPECIES OF MINNESOTA AND GENERAL 



REMARKS INTRODUCTORY TO SAME. 



In the following tables the student will find the names of all the species known to 

 occur in the Minnesota strata of the Trenton and Hudson River periods, excepting the St 

 Peter sandstone. To these are added a number that are likely to be found within tin- 

 limits of the state but are as yet known to occur only in the neighboring states of Wis- 

 consin, Illinois and Iowa. With these the total number of forms catalogued is 809. Species 

 described in the volume from other regions are not included in the list since they have no 

 bearing at present upon the points which the tables are intended to bring out These 

 tables show also the stratigraphic and geographic distribution of the species, while 

 the summary tables which follow the list show how the faunas of the various stratigraphic 

 divisions compare with each other and with those recognized in the Cincinnati, Tennessee, 

 N.-w York and Canadian Lower Silurian regions. 



