__ Enumeration of Fossils collected in the Niagara Limestone at Chicago, Illinois ; ivith Descriptions 

 of several New Species. By Prof. ALEXANDER WINCHELL and Prof. OLIVER MARC Y. 



s: 



ly* Read January 4th, 1865. 



JMORE than a year ago, some fossils came into our hands from the quarries in the south 

 part of the city of Chicago, Illinois, in a suburb known as Bridgeport, which seemed to pos- 

 sess an unusual degree of interest. We at once visited the place, and subsequently adopted 

 p measures to procure as complete a collection as possible of the fossils of the locality. Be- 

 lieving that an exhibition of the ancient fauna which once lived upon the spot would pos- 

 sess considerable geological interest, we have made note of every species which has fallen 

 under our observation, and, by an understanding with Mr. Worthen, the State geologist of 

 Illinois, offer the results of our studies in the following paper: 



The rock at the principal quarry is a limestone, which, to a considerable extent, is in a 

 broken and amorphous condition. The entire mass, in consequence of the partial or com- 

 plete destruction of the fossils, has assumed an extremely vesicular structure. The upper 

 portion seems to be somewhat magnesian; it is of a pale buff color, more massive than the 

 lower, and contains nearly all the species enumerated in the present paper. Its thickness at 

 the quarry is about eighteen feet. The lower portion is of a bluish color, generally harder 

 in its solid parts, but somewhat diversified with patches of an argillaceous character. It 

 has not been quarried to any considerable extent, and the excavations do not penetrate it a 

 greater distance than about four feet. It is only in this part that we find those interesting 

 species, Acidaspis Ida, Ischadites tessellatus, and Gomphoceras Marcyce. The whole mass of the 

 rock, both above and below, is a congeries of organic remains, three fourths of which are 

 reduced to an unrecognizable condition, and many of which have been totally or partially 

 dissolved out, showing, in some instances, the delicate tracery of the exterior, or compli- 

 cated internal structure, in an extraordinary state of preservation. 



We do not intend to be understood by what is stated above, of the upper and lower 

 portions of the exposure, that in our opinion we recognize here the line of demarcation 

 between two stages of the formation, not considering our data sufficient to justify a con- 

 clusion on this point. 



According to Mr. Worthen, the rocks at this locality are lithologically and paleontologi- 

 cally identifiable with the Leclaire limestone at the upper rapids of the Mississippi, near 

 Leclaire, Iowa, and Port Byron, Illinois. 1 Mr. Worthen states that a Bryozoan form resem- 

 bling Didyonema retiformis, Myalina mytiliformis, Strophomena depressa, a small Pentamerus re- 

 sembling P. galeatus, and three or four species of chambered shells belonging to the genera 

 Orthoceras and Cyrtoceras, are common to the Leclaire and Chicago limestones, establishing 

 an identity between the two, as he thinks ; while the Niagara age of the latter is shown by 

 the number of Niagara species which it contains. 



Professor Hall (Iowa Geol. Rep., p. 73,) had previously supposed the Leclaire limestone 

 might be the western equivalent of the Gait limestone of Canada West, though he subse- 

 quently recognized the evidences of its belonging to the age of the Niagara group, occu- 

 pying a position probably in the upper part of the group. 2 



1 Amer. Jour. Sc. and Arts. vol. xxxiii. p. 46, 1862. a Wiscon. Geol. Rep., pp. 67 et seq. and 446 el seq. 



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