SPECIES HAVING LIMITED VERTICAL EANGE. 285 



STRATIGRAPHIC RANGE OF SPECIES HAVING A RESTRICTED VERTICAL DIS- 

 TRIBUTION. 



The remaining . species of our flora may, on account of either their 

 specific sohdarity or their somewhat limited vertical range, be regarded as 

 compositely possessing a more direct and accurate chronologic significance. 

 In the following table is shown the summarized distribution of these 

 species in the bituminous fields of Ohio, Indiana, Illinois, and Pennsyl- 

 vania, and in the Northern Anthracite field, based on a personal examina- 

 tion of the collections that have formed the subjects of the principal printed 

 reports. Several of the species here tabulated are recorded in some of the 

 American literature relating to these collections as having a vertical range 

 greater than that shown in the table; but an examination of the specimens 

 serving as bases for the greater number of those extended records shows 

 that materials from vertically widely separated horizons have often been 

 assigned to the same species, although when closely inspected it is seen that 

 they represent entirely distinct species, and frequently also no transitional 

 or intermediate forms, varieties, or species have been found. Numerous 

 examples are seen among the specimens from the Pottsville series ("sub- 

 conglomerate" and "conglomerate"), which have been recorded under the 

 names of distinctly Coal Measures species. Those who may wish to con- 

 sult the extended distribution as recorded in the literature will find a nearly 

 complete compilation in the publications of the Second Geological Survey 

 of Pennsylvania.^ 



In the following table no account is taken of the variations or modifica- 

 tions which some of the species have undergone within the time of their 

 ascertained duration. 



The distribution of the species in Rhode Island is omitted on account 

 of lack of information relating to both the geographic and the stratigraphic 

 sources of much of the material. It would seem, however, from the large 

 number of species in the Rhode Island collections that are identical with 

 those in Missouri and the affinities of others, that a considerable portion of 

 the specimens from the former State may have come from a fossiliferous 

 horizon of perhaps not much later date than the fossils from Missouri. 



"See Reports of Progress, P, vol. iii, 1884; PP, 1880; and P i, vols, i-iii, 1889-90. 



