XIV THE PALEONTOLOGY OP MINNESOTA. 



"Several casts of spiral univalves; of a cirrus resembling the perspective; of an ampullaria, reserubl - 

 ing the camliculata ; imperfect impressions of a long spiral univalve, resembling the genus vioipara all 

 taken from the walls of a lead-bearing fissure near Dubuque; a univalve of the genus trochus (found in 

 the underlying blue limestone) and another, resembling a delphinula, found chiefly in the building rock. 



"I also found both in the cliff rock and in the blue limestone (but chiefly in the latter, of which it 

 is the characteristic fossil,) several species of strophmnena of Goldfuss. 



"Likewise, both in the cliff rock and in the blue limestone, several species of orthoceratites." 



The report is accompanied by a geological map of the region explored and several 

 sections, the most important of which is one from just below the mouth of Rock river 

 northeast through the Blue mounds to the Wisconsin river. This section shows the Coal 

 Measures above the Cliff limestone and separated from it by the shell stratum (i . e. the 

 Devonian ) ; immediately underlying the Cliff limestone is the blue f ossilif erous limestone 

 and below this are beds of red and white sandstone, which are followed by alternating 

 strata of Lower Magnesian limestone and more red and white sandstone. The lead-bear - 

 ing formation Cliff limestone is also called the Upper Magnesian limestone. The 

 average dip of the strata is 9 in a southerly direction. 



The report of Dr. Owen includes a report of Dr. John Locke in which carefully de- 

 tailed sections at Dubuque, Prairie du Chien and from the Blue mounds to the Wisconsin 

 river are given. Dr. Locke compares the lead-bearing rocks with the Cliff limestone of 

 Ohio. He gives twelve points of agreement between the Cliff limestone of Ohio and the 

 lead- bearing strata, the last of which is as follows: (p. 120) 



"The fossil remains found in the lead region agree with those found in Ohio. Some of them are as 

 follows: 



" I. Multilocular shells. Ammonitea and orthoceratites. 



"II. Crustaceans. Several species of calymene, asaphus, and isotelus. * * * * 



"III. Crinoideans. * * * * 



" IV. Mollusca. Spirifers, terebratulae and productse. A cast of several species of bivalves occurs. 

 * * * * No fossil appears to be more characteristic of this formation than these casts; perhaps rather 

 from their peculiar condition, than from the specific character of the fossil itself. 



"V. Zoophytes. Corallines are abundant in both regions; of cyathophylla, several species; of 

 calamopora (Goldfuss), several species; of catenipora, at least three species are nearly equally abundant. 

 The eschara (of Goldfuss) which is abundant on the Miami in Ohio, and which I once thought charac- 

 teristic of this stratum, seems to be limited to particular localities. I did not see it in the lead region." 



Dr. Locke seems to have been the first to parallelize the "Cliff limestone" of Ohio, a 

 portion of the Upper Silurian, with the lead-bearing rocks. He makes special claim to 

 this discovery in the Am. Jour. Sci., vol. xliii, p. 147 (1842). Although this idea was 

 accepted by Owen in this report and by Hall later, as well as by others, it was found 

 finally that the Cliff limestone of Ohio and Indiana did not embrace the lead-bearing 

 horizon. at all, but was separated from it by the Maquoketa shales. 



* 



Dr. Locke's section, plate No. xix, extending from the south fork of the Little 

 Maquoketa across the Mississippi to the Sinsinewa mound, represents a thickness of rocky 

 strata amounting to 550 feet, and covers all the Lower Silurian, put by him into the "Cliff 

 limestone;" although the Blue limestone is represented as somewhat below the water at 

 Dubuque where the section crosses the river. 



