256 SCIENCE PROGRESS 



this or that geologic epoch, the addition of the various results 

 should give some clue to geologic time. 



Further information could be obtained if we possessed fuller 

 information concerning the extent of particular local formations. 

 The structure of coal beds will illustrate my meaning very well. 

 If and when it is possible to map out the extent and structure of 

 particular beds, and of the intervening strata, it might be possible 

 to put together a connected history of that particular tract of 

 land. For this we require detailed information. We require to 

 know where and how a particular bed commences, its extent, its 

 manner of grading into other strata, and many other details. 

 We require to be able to make a model of the ground so as to 

 show the configuration of its strata in as much detail as possible. 

 We want a geologic map of some special tract of country which 

 will show, not only epochs, but small individual formations. 

 The detailed sections of various parts of a district require com- 

 parison and co-ordination. Then its history can be written. 

 Then we can compare the processes of the past with those now 

 going on, and form some idea of how, and in what space of time, 

 they occurred. The estimate of time would be rough, but, at 

 least, so far as it went, it would be by the reconstruction of 

 actual events. 



The idea will be made clearer if I utilise an example which 

 I have mentioned before. 1 I refer to coal beds. The view has 

 now received general acceptance that a considerable proportion 

 of these have been formed in situ. There are, no doubt, such 

 things as drift beds, but many of the coal beds, especially the 

 seams that are large and workable, undoubtedly represent the 

 actual sites of the old Carboniferous swamps which flourished so 

 largely and were so widespread. Some of these seams are of 

 enormous extent. There is, for example, the " Pittsburg," in 

 Pennsylvania, at least 12,000 miles in area. Why should it not be 

 possible to map out a coal-field in detail, to show roughly where 

 each particular seam begins and ends, where each divides, to 

 indicate the extent of each intervening layer of sandstone, shale, 

 or limestone, if and when the latter occurs ? 



Each successive coal bed indicates an advance and a recession 



of the sea. If and when this has taken place over large areas, 



events have occurred to which a minimum of time can be 



assessed, or, at any rate, some idea of the necessary time can be 



1 See article in Contemporary, Feb. 191 1. 



