HISTORICAL SKETCH. 



xliii 



the upper layers of the buff limestones of the Trenton group, " or "buff limestones near 

 the middle of the Trenton group," or "blue beds of the Trenton limestone below Carpenter's 

 quarry" (at Beloit). Sometimes the description involves such combinations as "hard lay- 

 ers of the bluish- buff limestones of the Trenton group, below Carpenter's quarry, " and 

 again "Lower Buff limestone of the Trenton group below Carpenter's quarry," or " in the 

 Buff limestone of the Trenton group at Carpenter's quarry." This variety of usage of 

 the terms Buff and Blue is explainable by reference to the abstract already presented, of 

 the report of Prof. Chamberlin in 1878. Prof. Whitfield describes and illustrates 36 

 species from the Trenton, being: lamellibranchs, 6; gasteropods, 16: pteropods, 1; cephal- 

 opods, 10; and crustaceans, 3. 



The following species are said to more particularly characterize the Galena limestone: 

 Receptaculites oweni Hall, Halysites catenulatus, Fischer, (two specimens from Rockton, 

 111. ) Lingulella iowensis Owen, Hemipronites americanus Whitf., Murchisonia major Hall, 

 Fusispira ventricosa Hall, Fusispira elongata Hall, Maclurea cuneata Whitf., and Mac- 

 lurea subrotunda Whitf. 



The Hudson River species illustrated are, five species of Radiata ( Chaste tes, Alveolites 

 and Monliculipora), eight species of Bryozoa, and ten of Brachiopoda. 



The general list of species given in this volume by Prof. Whitfield is enlarged and 

 reproduced in volume i, which was the last volume of the report to be published. It is 

 condensed below, from vol. I. 



Total species identified with the Lower Silurian, 278. 



COLUMN 1. Species common to the Hudson River and the Galena, 22. 



COLUMN 2. Species common to the Galena and Trenton, 64. 



Note. In each of these comparisons we may note the closeness of affinity by the ratio 

 of the common species to the smaller one of the faunas compared, and in this way we find, 



