332 MR ROBERT KIDSTON ON THE 



but, as the Hamstead plants are found both below and above these Radstock red 

 shales, it is clear that they existed during the deposition of these beds ; and further, 

 the few fossils which I have seen from them are similar to those of the Radstock and 

 Farrington series, I therefore conclude that the Upper Coal Measure red shales that 

 overlie the Middle Coal Measures at Hamstead are a northern extension of the red shales 

 which form such a well-marked horizon over a considerable portion of the Somerset 

 Coal Field. 



The Molluscan remains, for whose identification I am indebted to Mr John 

 Young, F.G.S., are of considerable interest, and bring forcibly forward some points 

 in their vertical distribution which do not appear to have received the attention they 

 deserve. 



Mr Meachem informed me that, through an accident happening to the collection, a 

 number of the specimens of shells were completely destroyed, and among these was 

 a Euonvphalus. The species examined and identified do not, therefore, represent the 

 whole fauna collected, but only those that are still preserved. 



The Mollusca identified are — 



Productus semireticulatus, Martin. 



Productus scabriculus, Martin. 



Edrnondia rudis, M'Coy. 



Schizodus, sp., allied to S. carbonarius, Portl. 



Modiola lingualis, Phill. 



Anthracosia Urei, Elem. 



Leda attenuate/,, Flem. 



Goniotites, sp., allied to G. excavatus, Phill. 



Leaving out of consideration those individuals which are only generically identified, 

 two of the species, Modiola lingualis and Leda attenuata, have been recorded from the 

 upper beds of the Calciferous Sandstone series.* P. semireticulatus, P. scabriculus, and 

 Edrnondia rudis are frequent in the Carboniferous Limestone series of Scotland, while 

 Anthracosia Urei is usually restricted to the Lower Coal Measures. 



Any one, judging of the age of the rocks from the Molluscan remains, would, without 

 doubt, class them as Lower Carboniferous, whereas they are undoubtedly of Upper Coal 

 Measure age. 



This case is not an isolated one, and Mr John Young has referred to such occurrences 

 in his paper entitled " Notes on the Occurrence and Range of Lingula in the Carboni- 

 ferous Series of the West of Scotland."' 1 Speaking of the apparent extinction and 

 reappearance of an organism in a higher horizon, the paper concludes with the following- 

 remark : — " Of such changes we have evidence in several of our coal seams, formed of 

 the remains of a terrestrial vegetation accumulated in swamps at or near the sea level, 

 and now found to be overlaid by a great thickness of fossiliferous marine strata. But 



* Mem. Geol. Survey of Scotland, Explan. to sheet 23, Lanarkshire Central District, p. 57. 

 t Trans. Geol. Soc. of Glasgow, vol. ii. p. 144. 



