AGE OF FLORA AND TIME OF EPEIROGENIC MOVEMENT. 295 



gressing Carboniferous sea. The testimony of the plants not only cor- 

 roborates the observations of the state geologists * as to the probable con- 

 cealment in that region of the earlier beds of the Coal Measures beneath 

 the overlapping margins of the later terranes, but it also approximately 

 fixes for the Henry County district the time at which the eroded Missis- 

 sippian shore passed beneath the encroaching sea. The unconformity 

 between the Jordan coal and the locally essentially subjacent Eocar- 

 boniferous terranes covers a period including the sedimentation of Meso- 

 carboniferous terranes attaining a maximum thickness of over 1,200 feet 

 in Pennsjdvania and exceeding 2,500 feet in southern West Virginia and 

 Alabama. 



VERTICAL RANGE OF THE MISSOURI SPECIES IN THE BRITISH COALFIELDS. 



One of the most interesting facts which appear to every student of 

 Paleozoic plants is the remarkable degree of identity between the plant 

 species of the Carboniferous in this continent and those of the old world. 

 The identities and obviously close intercontinental relationships are not 

 less striking than are the similarities in the elemental composition of the 

 flora of each successive stage and the essential general regularity in the 

 order of the sequence of the various floral associations. In the two fol- 

 lowing tables showing, in part only, the foreign distribution of the Mis- 

 souri species the first of these conditions very imperfectly appears, but 

 it is not within the limits of the present paper to further illustrate or 

 amplify either subject. 



The following table indicates the vertical range in the principal divis- 

 ions of the Coal Measures of Great Britain of (1) the species common to 

 Henry county and the British coalfields, and the range in the latter of 

 (2) a number of old world species whose relationships to ours are suffi- 

 ciently intimate to lend an inferential significance to their stratigraphic 



occurrence.f 



It will at once be seen in a glance at the accompanying table that the 

 greater portion of the identical species are found in the Middle Coal 

 Measures and the Upper Coal Measures of Great Britain. Only about 

 one-half as many are present in the Lower Coal Measures as in either of 

 the divisions just named, and these species are generally plants of wide 

 vertical range. Judged, therefore, by the numerical proportions, it would 

 seem that the Henry County flora is so equally bound to both the 

 Upper and the Middle Coal Measures as to suggest an intermediate posi- 



*See Winslow : Bull Geol. Soc. Am., vol. 3. 1891, pp. 109-121 ; Preliminary Report on Coal of 

 Missouri, 1891. p. 19 ; also Keyes : Am. Geologist, vol. xii, 1893, p. 100. 



1 For the British distribution of the species I am indebted to a valuable and critically pains- 

 taking memoir by Mr Robert Kidston, " On the Various Divisions of the British Carboniferous 

 Rocks as determined by their Fossil Flora." Proc. Royal Phys. Soc. of Edinburg, vol. xii, 1894, 

 pp. 183-257. w 



XLIV— Bull. Geol. Soc. Am., Vol. 8, 1896 



