AGE RELATIONS OF COAL-BALLS 



13 



*' floral break" first recognized by Kid- 

 ston in the English Carboniferous. 



One other important source of fossil 

 plant material comparable to that in 

 coal-balls is in the Calciferous Sand- 

 stone series of southern Scotland, The 

 Pettycur limestone on the Firth of 

 Forth in Fifeshire is most notable, par- 

 ticularly since a third species of Mazo- 

 carpon, M. petty curense, comes from this 

 locality. The age equivalence of this 

 limestone (a brecciated travertine ac- 

 cording to Gordon, 1909) is apparently 

 not precisely definable because it occurs 

 in a thick sequence of pyroclastic rocks 

 and beds that lack suitable zonal fossils. 

 Allen (1924) has given a rather detail- 

 ed section taken around the coast on 

 the north shore of the Firth of Forth 

 which must include the Pettycur lime- 

 stone, although the bed is not identified 

 as such. Apparently its position is 

 somewhere within the upper Oil Shale 

 group. Generally speaking, the Calci- 

 ferous Sandstone may correlate with 

 beds of Lower and in part Middle Mis- 

 sissippian age in America, which include 

 the Pocono-Price of continental facies 

 in the eastern Appalachians and marine 

 beds in the Illinois basin. 



DISCUSSION 



The Pennsylvanian of Illinois has 

 been correlated with that of the Ap- 

 palachian trough by Wanless (1939) 

 and others. As mentioned previously 

 there is some agreement of opinion con- 

 cerning correlation of the New Eiver 

 beds (middle Pottsville) with the West- 

 phalian A. Thus it is possible to arrive 

 at an estimate of the time interval 

 separating the Calhoun horizon (con- 

 taining Mazocarpon oedipiernum) and 

 the Great Coal-ball horizon from which 

 Mazocarpon shorense was described. 

 Since the latter horizon is not far above 

 the base of the Westphalian A, its 

 equivalent would be in the lower part 

 of the New River group in West Vir- 

 ginia. According to Wanless (1939; al- 

 so oral communication) this would cor- 

 respond, in Illinois, to some horizon 

 probably below the Battery Rock coal 

 of the Illinois Casey ville group. 



There is questions as to the proper cor- 

 relation of the upper part of the Mc- 

 Leansboro group in both the Appala- 



chian and mid-Continent areas. Tenta- 

 tive correlations hj Moore (1936, pp. 

 71, 144) suggest that the Missouri -Virgil 

 boundary is about equivalent to the age 

 of uppermost McLeansboro beds of Il- 

 linois and is somewhere near the Cone- 

 maugh-Monongahela boundary of the 

 Appalachian trough. Weller (personal 

 communication) has recently considered 

 that the McLeansboro beds may range 

 somewhat higher than this. 



Thus the disparity between time of 

 deposition of the two coal-ball horizons 

 in question is equal to the greater part 

 of the Illinois Pennsylvanian section, 

 including equivalents of much of Cone- 

 maugh, all of the Allegheny and Kan- 

 awha, and a considerable part of the 

 New River time intervals. The tendency 

 in the past has been to place the Illinois 

 McLeansboro beds higher in relation to 

 the European section than is indicated 

 on the chart (fig. 1), therefore it ap- 

 pears that the present estimate of the 

 time interval is a conservative one, and 

 the age discrepancy between these two 

 coal-ball horizons may actually be 

 greater. Mazocarpon pettycurense from 

 the Pettycur limestone is, of course, 

 much older than either of the Upper 

 Carboniferous species. 



The genus Mazocarpon appears there- 

 for to have a proved range extending 

 fairly well through the Carboniferous. 

 The Calhoun occurrence is by far the 

 youngest. The infrequency of reports 

 of Mazocarpon probably has been due to 

 lack of attention given to material from 

 which it might be identified. That this 

 is the case is supported by evidence 

 derived from other closely related 

 groups of plants, discussed later, which 

 are well known from intervening hori- 

 zons. The continuity of Mazocarpon 

 throughout the Upper Carboniferous is 

 important in that it shows more de- 

 cisively than was possible heretofore 

 that the sigillarians are a discrete group 

 of plants, distinct from other groups of 

 arboreous lycopods, such as Lepidoden- 

 dron, Lepidophloios etc. that are also 

 present in the same series of beds. As 

 such groups become better defined the 

 possibility of applying methods of phy- 

 logenetic paleontology becomes increas- 

 ingly more practical. 



