33G Correspondence — Mr. D. JL S. TTafsoii — J/r. 0. T. Jones. 



its top (if it 1ms one in Englnml) may be niftrketl by the dying out 

 of other species luid by the incoming; of a iliftVreut fauna. 



If Mr. Bryilone wants to introduce a new system of zonal 

 chissifioation for the Clialk. by all means let him try. but it is not 

 reasonable to tind fault with me for choosing 0. huiata as an index 

 of the Trimminj^ham zone merely because it does not satisfy his own 

 peculiar idea of what a zone and a zonal index should be. 



A. J. Jukes-Browne. 



AXTEEACOMYA IX THE RADSTOCK COAL-MEASURES. 

 Sir, — Whilst collecting at the Lower ^yrithlington Coal-pit, 

 ■working the Radstock Series of Coal-measures, I had the good 

 fortune to find several specimens of Peleoypods. As no shell 

 except Carhonicola atjniliiiu has been so far recorded from these 

 beds, I thought that it would be as well to record them. 

 Dr. Wheelton Hind has kindly identified theni as Anthracoviii(t 

 phillipsi, ^Vill.. and A. hxnccolatd, W. TTind. A. phiUipsi is typically 

 an Upper Coal -measure species, having been first found in the 

 Ardwick Series of Manchester. Tlie exact locality and horizon of 

 A. hxnceolata, previously represented only by the type-specimen, 

 are uukuowu, but the horizon, Dr. W. Hind informs me, is probably 

 high. D. M. S. Watson. 



MANCllKSTFJi UXIVEKSITY. 



THE GEOLOGY OF THE PLYNLIMMON DISTRICT. 



Sir. — For the past three years I have devoted my leisure time to 

 the detailed examination and mapping of part of the district 

 described by Mr. Walter Keeping many years ago.^ The district 

 examined extends southwards from the Plynlimmon range towards 

 the valley of the Ystwyth and westwards towards Aberystwyth. 



As the conclusions I have come to diverge considerably from those 

 previously published. I venture to think that a short summary will 

 be of some interest to readers of the Geological Magazine. The 

 chief results are the following : — 



The Plynlimmon range is a dome formed wholly or partlj' of 

 Bala rocks. The Lower Llandovery rocks, which are divisible into 

 several zones, wrap round them, and are followed towards the south 

 by the Upper Llandovery and Lower Tarannon rocks in more or 

 less orderly succession. The highest fossiliferous rocks met with 

 belong to the zone of Mouograptus crigtnts. They are followed by 

 thick grits which are probably on the horizon of the Talerddig Grits 

 of the Tarannon country. Hitherto rocks of this age have not been 

 recorded from this area. I hope shortly to publish my results in 

 detail. O. T. Jones. 



'2S, Jeem\x Street, London, S."W. 



' Quart. Journ. Gtol. Soc, vol. sxxvii, p. 141. 



