REVIEWS 545 



coals wrought in disconnected or somewhat isolated portions of the southern 

 anthracite field. The other, which concerns the question of general geologi- 

 cal correlation, is the acquisition of data for the determination of the age of 

 the Pottsville formation — z. <?., (a) the time interval represented by the type 

 section, and {b^ the equivalents, in a broad sense, of the formation in other 

 basins of this province and in other parts of the world. Incidentally also, 

 through the discovery in the Pottsville of floras already more or less com- 

 pletely known from isolated and uncorrelated terranes in other regions of the 

 United States, the way is opened to the proper reference and correlation of 

 those terranes with the Pottsville, or with portions thereof. 



As introductory to the consideration of the plant remains as a 

 means of geological classification there are presented a sketch of the 

 general geological structure of the southern anthracite coal field, a 

 description of the Pottsville formation in the typical locality, the com- 

 position of the formation, the coals contained, and their commercial 

 names as guide horizons. 



A type paleobotanic section of the Pottsville is then discussed, and 

 the groupings of beds are enumerated. The various species and their 

 observed distribution within the formation and in the field is given 

 in detailed tabulated form, in which all the species are listed, together 

 with their respective ranges. The floras of the several subdivisions 

 indicated are discussed in some detail. The correlative comparison 

 of the horizons of the southern field with those of the other anthracite 

 fields is of special interest. 



A considerable portion of the memoir is devoted to the description 

 of the most characteristic species of plants found in the Pottsville, 

 and to notes on many other species. 



One of the most surprising, as well as interesting, facts observed in the 

 study of the Pottsville floras is the large element that is common in the 

 latter and to the flora described by Sir William Dawson from the supposed 

 Middle Devonian beds of St. John, New Brunswick. In fact, taking into 

 view the entire flora of the Pottsville formation in the Appalachian province, 

 the identities in the composition of the floras are so great, with respect to 

 both genera and species, as to leave little room for doubt that we have in the 

 "Fern Ledges" at St. John beds of nearly the same age as the Pottsville 

 formation in Pennsylvania. On the whole, while recognizing in the Potts- 

 ville formation a group of terranes equal in rank to the Lower Coal-measures, 

 Alleghany series, etc., I do not favor a classification which relegates the 

 entire formation hard and fast to the Upper Carboniferous, but I even antici- 

 pate a possible necessity for its permanent division into two groups, the lower 



