RADSTOCK SERIES OF THE SOMERSET AND BRISTOL COAL FIELD. 409 



" The species in your list that I have not found in our Bassin du Nord, but 

 which occur in our Bassins du Centre, I have marked 'Superior' ; others, which 

 are found both in the Bassin de Valenciennes, but especially in its highest part, 

 and at the base of our Bassins de la Loire and Alais, as Sphenophyllum emar- 

 ginatwn and Sig. monostigma, or even extending into the highest beds, as Astero- 

 phyllites equisetiformis, Annularia stellata, Ann. sphenophylloides, and Alethopteris 

 Grandini, I have marked 'Inferior Superior' Others again, that I have only 

 known in the Bassin de Valenciennes and not in our Bassins du Centre, I have 

 marked 'Inferior,' among these last a certain number occur in the north of 

 France, towards the top of the Basin, that is to say, in the oil or gas-coal beds 

 at the Pas de Calais, which the Abbe Boulay has already shown, and which I 

 show in my turn, to be the highest part of the Bassin de Valenciennes. These 

 are Sphen. neuropteroides, Neur. Scheuchzeri, Neur. rarinervis, Dictyopteris 

 Munsteri, Pecopteris crenulata, Aleth. Serlii, Ulodendron majus, and Sigillaria 

 reniformis. What I have not marked as to horizon are those which I have not 

 seen in France, but Sphen. Grandini ( = Sphen. alata, Brongt. ) is from Geislautern, 

 that is to say. from the summit of the middle zone or from the base of the 

 highest zone of the Saarbriick Beds ; Corynepteris erosa is from Saxony. These 

 two indications agree with what I have said already. 



" On the other hand, I remark the absence of several species which with us 

 are abundant in the Upper Coal Measures, particularly Sphenophyllum oblongi- 

 folium, Sphenophyllum angustifolium, Sphenophyllum longifolium (to which my 

 Sphenophyllum Thoni should, I now believe, belong), Neuropteris cordata, Odon- 

 topteris Reichiana, Dictyopteris Brongniarti, Callipteridium pteridium ( = Pec. 

 ovata, Brongt. = Call, mirabile, Rost., sp.), Pec. arguta ( = Fil. famiinaformis, 

 Schl.), Sigillaria Brardii, and Sigillaria spinidosa. 



" From this, Radstock represents, in my opinion, a horizon (niveau) that we have 

 not in France, but corresponds to the interval between the end of the Coal Deposits 

 in the north of France and the beginning of the Coal Fields of the centre." 



In a later letter M. Zeillek further says — " The mixture they (the Radstock 

 Series) present of Upper Coal Measure species with Lower Coal species is un- 

 questionable, but I do not at all mean to say by that that they are equal both 

 to all or part of our Lower Coal (or more exactly our Middle Coal) and of our 

 Upper Coal; in my opinion they are intermediate between the two, and are 

 situated immediately above our highest beds of the north of France and below 

 our lowest beds of St Etienne, Gard, &c. ; perhaps their base is equivalent to 

 the summit of the first and their summit the equivalent of the base of the latter, 

 but on the whole I think their position is between the two," 



