HISTORICAL SKETCH. XXXV11 



Silurian gasteropods, " Receptaculites, Orthis, Lingula " and probably Discina, " cyatho- 

 phylloid corals, Tentaculites, Spirifers, trilobites, and Orfchoceras.* 



James Shaw. 



1872. Geological Survey of Jllinois, vol. v, Geology, by A. H. WORTHEN and JAMES 

 SHAW. Springfield, 1873. 



The preliminary chapter in this volume, on the "Geology of Northwestern Illinois," 

 and several others describing several counties more specially, in that portion of the state, 

 are by Mr. Shaw. These counties are contiguous to that part of Iowa and of Wisconsin 

 which embrace the lead region of the Northwest, and have a bearing on the nature and 

 extent of the Lower Silurian strata considered in this volume of the Minnesota survey. 



The Hudson River shales, above Savanna, are said to have an exposed thickness of 80 

 feet, and to reach a total thickness of about 100 feet. 



In the Galena the characteristic fossil is termed Receptaculites sulcata, the "sunflower 

 coral. " 



Below the Galena "comes the Blue limestone, or Trenton limestone proper, of the 

 earlier western geologists. It is now regarded as the middle division of the Trenton 

 group, the Galena above and the Buff below both being regarded as members of the Tren - 

 ton." The Blue limestone has a thickness from 45 to 60 feet, and the Buff generally about 



20 feet. 



A. H. Worthen and F. B. Meek. 



1875. Geological Survey of Illinois. Vol. vi. Paleontology, Section n. Descriptions 

 of Invertebrates, Springfield, 1875. A few species of Lower Silurian fossils are described 

 in this volume. They are from Dixon, Mount Carroll, Savannah and Oswego, Illinois. 



R. P. Whitfleld 



1877. Preliminary descriptions of new species of fossils from the lower geological forma- 

 tions of Wisconsin, by R. P. WHITFIELD. Ann. Rpt. Wisconsin Geol. Survey for 1877; 

 Madison, 1878; pp. 50-89. 



In this paper sixty-five new species are described. Those from the Trenton period, 

 twenty-four in number are as follows: 



Trematopora annulifer, Hudson River shales. Trematopora granulata, Hudson River shales. 



Fenestella granulosa, Hudson River shales. Fistulipora solidissima, Hudson River shales. 



Fistulipora fens, Hudson River shales. Ch/vtetes fusiformis, Hudson River shales. 



Monticulipora rectangularis, Hudson River shales. Multiculipora punctata, Hudson River shales. 



Monticulipora multituberculata, Hudson River shales. Alveolites irregularis, Hudson River shales. 



Hemipronites americana, Galena. Strophomena kingi, Hudson River shales. 



Rhynehonella perlamellosa Hudson River shales. Cypricardites megambonus, Buff limestone. 



Metoptoma perovalis. Lower Blue limestone. Trochonema beloitensis, Buff limestone. 



Clisospira occidentalis, Buff limestone. Maclurea cuneata, Galena. 



Maclurea subrotunda, Galena. Eucania (Tremanolus ?) buelli, Upper Buff limesone. 



Hyolitlies baooni, hard bluish-buff layers. Orthoceras (Actinoceras) beloitense, Buff beds. 



Bellerophon witconsinenxis, blue beds of Trenton limestone. 



Gyroceras duplicostatum, Trenton limestone and bluish-buff beds. 



These descriptions are republished in vol. iv of the final report of the Wisconsin sur- 

 vey, 1882 with illustrations. 



Mr. Hurllnit, still resides at 'Rochester, Minn. The writer retains a vivid recollection of his cordial and generous wel- 

 come by Mr. Hurlhnt when, in 1872, the present survey was Inaugurated. 



