CORRELATION OF STRATA. XC1xX 
preceding shales of the Black River group it thins rapidly in a southeastern direction 
from Goodhue county, being very thin in Olmsted county and scarcely, if at all, repre- 
sented in the southern part of Fillmore county. 
The lower eight feet at St. Paul contains great numbers of Zygospira recurvirostra 
and Rhychotrema increbescens, while Pachydictya elegans is abundant and characteristic of 
this portion. Taking the bed as a whole the Bryoza make up a large part of its fossils, 
10 of the 36 species being also restricted to it. Nextcome the Gastropoda with 29 species, 
the Brachiopoda with 238, and the Lamellibranchiata with 13. The principal characteristic 
fossils are Callopora ampla, C. goodhuensis, Prasopora insularis, Eridotrypa mutabilis, Stro- 
phomena scofieldi, Orthis meedsi, Clitambonites diversa, Vanuxemia hayniana, Tetranota 
bidorsata and Arges wesenbergensis var. paulianus. A small variety of Plectambonites sericea 
(minnesotensis Sardeson) is also very abundant. Receptaculites oweni is occasionally met 
with in the uppermost layers of this bed at St. Paul. In the description of the species 
this bed is always called the Galena shales. Thatterm, however, is not entirely restricted 
to the Clitambonites bed but occasionally includes also the lower part of the next bed. 
Fusispira bed. This is by far the most important of the three or four beds of the 
Trenton in Minnesota. Outcrops are numerous in Fillmore, Olmsted, Dodge and Goodhue 
counties, and fossils, most of them well preserved, are abundant in many of the layers. 
As already pointed out, the lithologic character of the bed varies considerably at 
different localities in the counties mentioned. (See sections 3, 4, 7 and 8.) The lower 
portion only is fairly constant, consisting, wherever this part has been observed, of soft 
shales and four or five, often irregular or lenticular, layers of crystalline limestone, 
varying in thickness from one to ten inches. These layers are crowded with fossils 
(mostly Bryozoa and Brachiopoda) many of which are restricted to the horizon. Being 
a persistent and easily recognized stratum it should have been separated and given a 
distinct name, but several reasons, chief among them the fact that we could not satisfy 
ourselves respecting the upper limit, have caused us to refer it provisionally to the 
Fusispira bed. Dr. Sardeson has, we believe, included it in his Camarella bed, which he 
gives a thickness of 30 feet.* He does not mention the limestone layers that occur at 
intervals in the lower 10 or 12 feet, and which lie directly upon the Clitambonites bed, but 
characterizes the bed according to the crumbling argillaceous limestones resting on them 
and which contain Parastrophia hemiplicata and Cyclospira bisulcata. The latter, as will be 
shown presently, does not deserve to be separated from the next series of strata which Dr. 
Sardeson calls the ‘‘ Lingulasma bed,” nor can we, for the reason given, justly restrict the 
use of the name Camarella bed to the 10 or 12 feet of strata immediately following the 
Clitambonites bed. Really, Dr. Sardeson’s name must be thrown out altogether for the 
simple reason that, according to the investigations of Winchell and Schuchert, and those 
recently published by Hall and Clarke,+ one of his supposed Camarellas proves to belong 
to the new genus Parastrophia, H. & C.,{ while the other is the type of another new genus 
* It is possible that we are mistaken and that Dr. Sardeson really regards the bed as the upper member of his 
Orthisina bed (Clitambonites bed of this book). Again it is possible that thelayers in question were entirely overlooked 
by him. (For abstracts of Sardeson’s papers see pp. xlvi and xlvii of the Introduction to part I of this volume.) 
+ Paleontology of New York, vol. VIII, pt: 2, fasc. i and ii, 1893. 
+ The species of this genus are referred provisionally to Anastrophia in this volume, pp, 382, 383. 
