582 MR. H. BOLTON, F.E.S.E., ON [June, 1904. 



equally typical blue shale, there is a great lithological 

 difference, implying an equally great difference in origin. 

 The mineral constituents of a black shale are finer, more 

 bituminous and coherent than those of a blue shale, and the 

 latter is often more or less micaceous. 



It seems natural to assume that the areas of deposition of 

 black shales were areas of almost stagnant water into which 

 only the finest particles of mineral matter could be carried, 

 and where deposition was very slow. 



Probably such areas were lagoon-like in character, pos- 

 sessing an intermittent connect' on only with freely moving 

 waters, and, bearing in mind their common position over 

 the coal, it may well be that the areas represented portions 

 of the coal forests which had become submerged by greater 

 growth at their edges, blocking the natural drainage and 

 converting the interior into swamps in which the vegetation 

 died, so giving place to extensive shallow lagoons, having a 

 very slight circulation of the contained water. 



The presence of the teeth, scales, and defensive spines of 

 the large predatory marine fish of the Coal Measures, such 

 as Megalichthys and Rhizodopsis sufficiently indicate that 

 these areas of deposition were not under fresh water, but 

 possessed at times sea connections. 



It must not be lost sight of however, that the Middle 

 Measures do not possess, except in one strange and solitary 

 instance, a clear and strong marine phase. This, the well 

 known, but little understood " Marine Band," seen in the 

 river Tame at Dukinfield, furnishes by its isolation, we 

 think, the most conclusive testimony of a greater development 

 of what may be termed the lagunal phase in the period 

 represented by the Middle Measures, than in that of the 

 Lower series. One other point must be mentioned before we 

 leave the black shales. Where Anthracosia (olim Carbonicola) 

 occur in them, they usually do so in large groups or even 



