544 REVIEWS 



The fact of the presence of numerous Helderbergian species in the fauna 

 of the Oriskany of Becraft Mountain, as an integral part of that fauna, not a 

 casual intermixture, is sufficient demonstration that the fauna of the Helder- 

 bergian became modified in its continued existence b}' the departure or 

 extinction of certain of its species only. A fair percentage kept the field up 

 to the time of and pending the incursion of species of the early Oriskany. In 

 this way the former became a true and proper part of this new fauna with 

 whose indicial species it coexisted throughout the remainder of its duration. 

 A modification so gradual as to permit such an uninterrupted existence can- 

 not sever the close relation of the one fauna in its entirety to the other. It is 

 therefore a natural corollary from the account given of the Oriskany fauna, 

 to consider briefly the relation of the organic assemblage constituting the 

 typical and normal Helderbergian to the Devonic type of organic life, and 

 that formation in its relation to the Devonic system. 



Arguments are adduced from the intrinsic characters of the fauna, 

 from correlation, and from stratigraphy. 



3. Of very different nature is Mr. White's work on the plants of the 

 Pennsylvania Coal-measures. The stratigraphical interval which he 

 considers is occupied by the Pottsville formation, Pottsville series, or 

 Pottsville conglomerate. It is described as a series of largely arena- 

 ceous beds of variable thickness which in eastern Pennsylvania lies 

 between the Maunch Chunk red shale, or distinctly Lower Carbonif- 

 erous, and the lower productive Coal-measures, or distinctly Upper 

 Carboniferous. 



The investigation was intended to establish three propositions : (i) 

 The exploitation and elaboration from, a stratigraphic standpoint, of 

 the fossil plants of the Pottsville formation in the type region of the 

 southern anthracite coal field ; (2) the critical analysis and compara- 

 tive study of the plant material collected, with a view to the discovery 

 of the existence of. any natural paleontological subdivisions, zones, or 

 horizons, and their paleontologic characters, or the species of strati- 

 graphic value ; (3) the discovery of the paleontologic limits as differ- 

 ing or as agreeing with the lithologic limits of the type section, and 

 the consequent paleontologic definition of the formation. 



The main aim of the investigation is the paleontologic definition 

 of the terrane. 



Two other, largely concomitant, results that are either economic or sci- 

 entific in their nature have also been reached in the process of the elaboration 

 of the fossil plants of the formation in the typical region. The first, of some 

 economic interest, is the correlation of the groups of beds, or of individual 



