528 Correspondence — Rev. A. Irving. 



THE CAEBONIFEROUS AND JURASSIC SYSTEMS OF EUROPE. 



Sir, — The valuable paper by Mr. Twelvetrees in the Geol. Mag. 

 for September must be welcomed by all who are interested in the 

 attempts which some of us are making to determine the true rela- 

 tions of the groups of strata which occur in the European area 

 between the Carboniferous and the Jurassic Systems. Its special 

 value arises from the fact that it embodies the observations of a 

 gentleman who has had opportunities, such as are offered to very 

 few geologists of our country, for making a direct acquaintance with 

 the important and extensive area to which the paper refers. No 

 one can have felt more than myself the imcertainty (not to say ten- 

 tativeness) of any judgment which can be formed at second-hand 

 from the lengthy and often vague description given by the great 

 master Murchison, whose great work still remains for western 

 geologists the chief source of information available with reference 

 to the Eussian area. Mr. Twelvetrees' observations go further, I 

 think, than anything which has as yet been published in this country, 

 to throw light upon several points about which many of us must have 

 felt much uncertainty ; and for my part I hasten to take this oppor- 

 tunity of thanking him (as well as for his courtesy in allowing me 

 to read his MS. before it appeared in print) for setting me right 

 upon the matter of the recurrence of the limestone deposits in the 

 Eussian ' Permian ' Series. I may also perhaps be allowed to point 

 out the important bearing of his paper as seeming to justify a 

 preference for regarding the German Dyas as the type of the 

 European rocks of the age in question rather than the Eussian 

 Series ; a preference which I have already expressed in my recent 

 paper on tlie " Classification of the European Eocks known as Dyas 

 and Trias." I will only now direct attention to the importance of 

 the series of Sandstones, Marls, etc., which occur in the Orenburg 

 country above the Magnesian Limestone formation, which, by the 

 way, appears to be much more completely differentiated in that 

 district than in the strictly 'Permian' region further to the north. 

 The resemblance in many respects, though there cannot be said to 

 be identity, between these and the 'Lower Bunter' of many parts 

 of Germany (which are, it should be remembered, stratigraphically 

 conformable with the underlying Zechstein Formation in Germany 

 as well as in Eussia), is of great importance. It would be premature 

 at the present to attempt to say what is their definite position in the 

 whole series ; but facts so far seem strongly to suggest the inference 

 that they are in sort a transition series between the Dyas and the 

 Trias, and this conclusion is borne out by more recent results 

 obtained by Alpine geologists. 



I ought not to conclude this without acknowledging the kindness 

 and courtesy of M. Marcou, whose many years' work on these 

 systems ought to receive more attention than it has done from 

 English geologists ; in particular, reference may be made to papers 

 by that gentleman (1) in the Bulletin de la Societe geologique de 

 France, 2nd Serie, t. xxiii. ; (2) Ihid, t. xxvi. ; (3) Ihid, t. xxiv. 



"Wellington College, Wokingham, a Irving 



Sept. liih. 



