Rev. Dr. Irving — On the Younger Red Rocks. 363 



the fifth, and also Quenstedt, Jura, pi. 21, fio;. 8. This is the 

 Margaritatus-zone form. Oppel considers that Zicters's species is 

 the Obtusus-zone form. The diiference between them seems to be 

 chiefly one of coiling, difficult to appreciate except in the handling 

 of specimens. 



At page 289 Pompeckj states in reference to Cymhifes and an 

 opinion of mine that Ammonites with " normal " body-chambers 

 ("concentrically umbilicate ") cannot be the descendants of those 

 with abnormal body-chambers ("excentrically umbilicate," S. S. B.). 

 In making this assertion he has overlooked Dactylioceras and 

 Stephanoceras, both examples of the earlier inheritance of " excentric 

 nmbilication" — the result of ancestral " abnormal " body-chambers — 

 producing "concentric umbilication." After all, the so-called abnor- 

 mality is a very normal feature of phyletic development ; and the 

 incorrectness of Poinpeckj's statement I hope to prove at another 

 opportunity. 



Y. — Twenty Years' Work at the Younger Eed Eooks.^ 

 By the Kev. A. Irving, D.Sc, B.A., F.G.S. 



HAYING made my first acquaintance with that puzzling series 

 of strata which bridges over the vast interval of geologic 

 time between the Carboniferous and the Jurassic in the Nottingham 

 district during a residence of eight years in the good old town 

 (see Proc. Geol. Assoc, vol. iv. ; also Quart. Journ. Geol. Soc, 

 November, 1875), the meeting at Nottingham seems a fitting 

 occasion for summarizing the results of further work in con- 

 nection with those rocks, as opportunities have offered, during 

 the last twentjr years. Those investigations have extended to other 

 parts of the Midlands, the Severn country, to Central Germany, 

 the Eastern Alps, and to Devonshire. 



As Reporter to the Sub-Committee of the International Geological 

 Congress for the " Permian and Trias," I had unusual facilities 

 for correlating the results of my own work in the field with those 

 of other workers. For this reference may be made to the Report 

 issued by the Congress. 



In a paper on the " Classification of the European Rocks known 

 as Permian and Trias" (Geol. Mag. Dec. II. Yol. IX. 1882), I 

 discussed more at length the results obtained down to that date, 

 with the aid of the German literature of the subject, my own 

 observations in the German and English areas, and the assistance of 

 Prof. Jules Marcou. These results may be briefly stated as tending 

 to establish for the European area generally the definite existence 

 of two independent systems, the one (the Permian or Dyas) marking 

 the close of the Palaeozoic history of the European area, with which 

 it is connected by its fauna and flora ; the other (the Trias) forming 

 the base of the Secondary series of rock-formations. I was, there- 

 fore, compelled to abandon the view as to the continuity of the 



^ A paper read at the Nottingham Meeting of the British Association in 1893 

 (Section C). 



