334 MR ROBERT KIDSTON ON THE 



but these are succeeded by rocks in which many of the old species have disappeared and 

 new species take their place by the side of the survivors. 



This state of matters maintains throughout the whole of the Coal Measures, and fur- 

 ther there does not seem to be the same complete disappearance, and then after a time a 

 reappearance of the same old forms, as in the case of the Mollusca, but instead, a constant 

 gradual change. This gradual change is, however, so marked, that it leaves a most sure 

 and certain stamp for the recognition of the comparative age of the rocks in which the 

 fossils occur. This leads me to believe, and every additional experience confirms this 

 opinion, that for the classification and correlation of the rocks of the Carboniferous 

 Formation, the evidence derived from plants is more reliably conclusive, and less liable 

 to variation, than that derived from animal remains. 



While speaking on this subject I might add further, that from the base of the Car- 

 boniferous Formation to the base of the Millstone Grit, the flora has a fades peculiar to 

 that period, and of the many species of plants occurring in Lower Carboniferous rocks 

 in Britain, it is very doubtful if any species pass into or above the Millstone Grit. 1 

 have seen slight evidence to think there may be one exception, but as far as I at present 

 know, only one.* 



From the Millstone Grit, though the difference of the flora is sufficiently clearly 

 defined to admit of a satisfactory threefold division of the Coal Measures, there is no 

 such sudden break as occurs between the Lower and Upper Carboniferous, nor does a 

 sudden break take place even at the top of the Upper Coal Measures, for several of the 

 Upper Coal Measure plants pass into the Permian Formation. 



For the facilities I have had given me for examining and describing the Hamstead 

 fossils, my thanks are due to Mr J. Meachem, Manager of the Hamstead Colliery, and 

 especially are they due to Mr Fred. G. Meachem, by whom the records of the sinking 

 were kept, and from whom I have received the particulars contained in the section given 

 on pp. 318-19. I am also indebted for assistance to Mr H. Insley, Ashton. 



It is to be hoped that all who have similar facilities for collecting the fossils met with 

 in Pit Sinkings and other mining operations, will avail themselves of these opportunities, 

 as such collections as that made at the Hamstead Colliery, where the horizon of each 

 specimen has been carefully noted, are of the utmost importance in working out British 

 Palaeontology. 



* I exclude Stigmaria, which is the root of several Lycopods, and as none of the Lower Carboniferous Lycopods 

 pass into or above the Millstone Grit as far as I know, Stigmaria, being the root of any one of these Lycopods 

 (Lepidodendron, Sigillaria, Lepidophloios) cannot be regarded as a true, individual species, and though these Lower 

 Carboniferous Stigmaria are individually undistinguishable from the Stigmaria of the Upper Carboniferous, they 

 cannot be regarded as specifically the same. 



