GEOLOGY. 317 



coal stratum, the lower beds in a basin being least rich in fossil plants, 

 the number of species associated with each sometimes not exceeding eight 

 or ten. 



It is but a few years since the first coal mine was opened in this region, 

 and up to the present time so little of the field has been thoroughly ex- 

 plored that it is quite too early to attempt to estimate the number of species 

 which are here fossilized. He had, however, already formed a catalogue 

 of about 150 distinct species, and had imperfect specimens of many more, 

 all collected from about half a dozen localities within a few miles of each other, 

 and within a vertical range of less than a hundred feet. From the num- 

 ber of species already collected, taken in connection with the fact that the 

 plants of a former world had somewhat the local habitat of those of the 

 present day, each coal mine having a florula in some respects peculiar to 

 itself, and each new mine that is opened furnishing new species, it is evi- 

 dent that the fossil flora of this limited district is remarkably rich. 



The fossil plants of this region are distributed among forty-one genera. 

 Dr. N. said, that a catalogue of these genera, which he presented, gave a 

 very good generic picture of the flora of the base of the productive coal 

 measures, at least in Ohio that it was characterized by a large number of 

 species of Sphenopteris, Calamites, Sigillariee and Lycopodiaccc that it 

 contained representatives of nearly all the genera of the carboniferous pe- 

 riod, and a large proportion of the most highly- organized plants of that 

 era. 



For the comparison, so far as made, between the fossil plants of the 

 lower and upper parts of the productive coal measure in Ohio, it would 

 seem that there had been a gradual change in the vegetation of the same 

 surface, both generic and specific the species of the older beds, almost 

 without an exception, being succeeded by others ; while the generic 

 changes were confined to the extinction of a small number with the in- 

 troduction of others, and a different numerical relation of species prevailed 

 at the different periods. 



Brongniart noticed in the coal fields of France that Calamites and 

 Lepipodendra were most abundant in the lower beds ; Sigillaria in the 

 middle and upper beds ; Asterophyttites, and especially Annularia, in 

 the upper coal strata. 



Dr. N. had found in Ohio that Calamites, Lepidodendron, Sigillaria and 

 Sphenopteris were most abundant in the lower beds. Cyclopteris, Annula- 

 ria, AsterophylUtes, Xeuropteris, Pecopteris were most numerous in the 

 middle and upper beds. Psaronius peculiar to the upper. That, as far as 

 his observation had extended, the place of Alethopteris lonchitidis was at 

 the base of the series. A. Serlii, Neuropteriscordata Pecopteris arborescens, 

 and Cyathea, Sphenophyllum Schlothimi Dictyopteris obliqua the middle 

 and upper beds, &c. 



Dr. N. said that, in the comparison of American with European fossil 

 plants, a very large proportion of the species collected here were regarded 

 as identical with those of Europe. He thought the matter required a 



