632 Scientific Proceedings, Royal Dublin Society. 



Methods available for locating concealed Coal Basins. 



Given a series of Mesozoic and Cainozoic rocks known to rest upon a 

 varied Palaeozoic floor, there are several sources from which we may obtain 

 evidence on which to base conclusions as to the composition, structure, and 

 form of the floor. The most obvious is to study the Palaeozoic rocks in 

 adjoining areas where they are exposed, and laying off' in these areas the 

 formations and structural lines, project them as far as we dare into the 

 concealed areas. This has its limitations, however, for structural lines do 

 not go on for ever, nor do they necessarily follow straight lines or logical 

 curves which can be depended upon. We have recourse next to the principle 

 of posthumous folding. This principle, first put forward by Godwin-Austin, 1 

 and used by him in his prediction of the Dover Coalfield, embodies the idea 

 that the lines of folding in the newer rocks tend to follow along similar lines 

 of folding in the older rocks of the floor, syncline generally following on 

 syncline and anticline on anticline. I use the expression " tend to follow " 

 with deliberation, because, to assume that every synclinal basin in the newer 

 rocks marks the site of an older syncline in the Palaeozoic floor, would be 

 equivalent to assuming that folding never takes up new lines on the earth's 

 surface, which is obviously absurd. Where the principle comes in most 

 usefully is in the case in which an anticline or syncline in an exposed portion 

 of the Palaeozoic floor can be traced beneath the Mesozoic cover, and its 

 course beneath the cover can be shown to be marked by a corresponding 

 anticline or syncline in the Mesozoic rocks above. The further course of the 

 post-Mesozoic fold can then be relied on to indicate with fair certainty 

 the course of the older fold, on which it has been shown to have followed 

 posthumously. It was a case of this kind of which Godwin- Austin availed 

 himself in the prediction of the Dover field. 



A further source from which conclusions can be drawn is the variation as 

 regards thickness and composition in the Mesozoic sediments. Elevation 

 along an old anticlinal axis or depression along a syncline, continued during 

 deposition, leads in the one case to local thinning of the sediments and in the 

 other to local thickening. Hence when we observe, in the successive members 

 of a series of strata, either thickening or thinning, we may draw conclusions 

 as to synclinal or anticlinal movement, which may be posthumous on an old 

 axis of depression or elevation. Further, the coming in of coarse or con- 

 glomeratic beds in a given direction may indicate the. contemporaneous 



: R. Godwin-Austin : On the possible Extension of Coal Measures beneath the 

 South-Eastern Fart of England. Quart. Journ. Geol. Soe., vol. xi, p. 533, 1855, and 

 Rep. Coal Commission, 1871, vol. ii, p. 424. 



