682 ME. H. BOLTON, F.E.S.E., ON [-^-Ug., 1904. 



until the whole fauna is considered in its horizon and zonal 

 aspects. One point, however, may be suggested as worthy 

 of consideration before subdivision is attempted and this is, 

 the question whether the flora or the fauna ought to be 

 taken as the true index to the sequence of Coal Measure 

 development. We are inclined to think that the fauna will 

 furnish the most satisfactory and rational standard for 

 several reasons. Chief of these is the fact that the faunal 

 development is closely connected with and cannot readily be 

 separated from the sequence of deposition. The vast bulk 

 of deposits in the Coal Measures are of marine, lagunal or 

 estuarine origin, the coal seams representing interludes of 

 varying length in point of time, but being in themselves 

 neither regular or naturally successively progressive. The 

 fauna would we know, rapidly respond to changes of 

 conditions, or of deposition, flourishing when conditions 

 were favourable and migrating or being starved and 

 attenuated when the conditions were unfavourable. In either 

 case, the continuity of life and development would not be 

 easily destroyed, and we should be more likely to find in the 

 case of the fauna, and the deposits in which they occur, a 

 well ordered continuity and developmental sequence, than in 

 the case of the coal forests, which were intermittent in 

 character, more inert to outside influences, and more 

 dominated by local and special conditions. 



That there was every likelihood of a progressive botanical 

 development is very likely, but the relation of the coal plants 

 as a whole to the Coal Measure series of deposits seems to us 

 a minor one as contrasted to that of the fauna which was at 

 once more sustained, more widespread and altogether more 

 readily responsive to change. 



If we briefly pass in review the fauna of the Upper Coal 

 Measures we shall note how fully, as we have previously 



