52 SECTIONAL ADDRESSES. 



frequent intercalations of marine strata — generally of limestone — which 

 is again milike the North Sea peat-fields. 



In the Yorkshire Coalfield — I hope I may be forgiven for styling 

 the coalfield extending from Leeds to Nottingham by the short title 

 ' The Yorkshire Coalfield ' — in the Yorkshire Coalfield, then, marine 

 intercalations are represented by beds of shale of extremely fine, blue, 

 unctuous, almost textureless character. These are never moi'e than 

 20 ft. in thickness, though it would not, perhaps, be quite fair to judge 

 by this relatively small thickness that the mai'ine incursions, though 

 not infrequent, were of proportionately short duration. 



The Coal Measures. 



i he succession of strata in a coalfield exhibits a considerable 

 diversity. Shales — the laminated muds of the old lagoons and swamps — 

 are the predominant elements. These vary much in texture from 

 coarse sandy and micaceous deposits, scarcely separable from actual 

 sandstones, through finer and finer materials to the ' marine bands ' 

 already referred to. 



The sand — now sandstone — beds are second in bulk only to the 

 shales, and it is interesting to observe that two principal stratigraphic 

 forms are presented. There are, first, the broad sheets extending 

 over hundreds or even thousands of square miles — for example, the 

 EUand Flags are recognisable by their position in the sequence 

 throughout the coalfield from Leeds to Nottingham; their equivalent 

 has been identified in Lancashire and with much probability in 

 North Staffordshire. Whether it reappears in North Wales is doubt- 

 ful, but its total area must certainly extend to several thousands 

 of square miles. No signs of marine life accompany it anywhere, but 

 in the northern part of its range it is surrounded, either directly or more 

 commonly with an interval of twenty or thirty yards, by a coal-seam — 

 the Better Bed, renowned for its purity and for the very valuable fire- 

 clay that accompanies it. Within or directly upon the top of the rock 

 was found the magnificent stigmarian root now in the Manchester 

 Museum. The evidence, positive and negative, proves the Elland Flags 

 to be of the delta flat type. No decisive indication of the direction of 

 the stream has been sought, though the analogy of the great sandstones 

 of the Millstone Grit series tempts me to conjecture that it was from 

 N. or N.E., and this surmise is strengthened by the occurrence of 

 the coal-seam in that direction and not to S. or S.W., and we may 

 picture a great sandy delta growing by its edge southward and west- 

 ward with a peat-swamp establishing itself on the higher parts. 



Lesser sandstones of the same general types are of frequent occur- 

 rence and bear the same general interpretation. 



In the other principal stratigraphic form the sandstones are of more 

 limited extension, especially in what I take to be the width of the bed. 

 This type is often called lenticular, but the adjective is a bad one, for 

 such a bed is in fact shaped morei like the bean-pod than the bean. 

 Beds of this character I interpret as the infilling of channels cut in the 

 deltaic flats. 



Two lithological types peculiar to strata of the Coal Measure facies 



