Br. C. Struchnann — The Jura of Hanover and England. 547 



to certain recent memoirs, sucli as that " On the Corallian Eocks of 

 England," by Messrs. Blake and Hudleston ;^ that " On the Kimmer- 

 idge Clay of England," by the Rev. J. E. Blake,^ and the important 

 paper " On the Portland Rocks of England," by the latter author.^ 



In using the palasontological details given in these and other works 

 on the English Upper Jurassic rocks for the formation of a com- 

 parative table of common fossils, M. Struckmann has accepted only 

 those species about the determination of which there was no doubt, 

 so that there is no room for erroneous results arising from differences 

 of interpretation. On the whole he has adopted the subdivisions 

 established by the English authors in the Upper Jurassic rocks ; 

 but he has united their Lower Calcareous Grit (Nothe Grit) and 

 Lower Limestone (Nothe Clay, Hambleton Oolite) with the upper 

 region of the underlying Oxfoi'd Clay (zone of Ammonites hiarmatus) ; 

 and has also combined the Middle Calcareous Grit, the Coralline 

 Oolite, and the Coral Rag in a single division. A part of the Coral 

 Rag, however, may be the equivalent of the Supracoralline Beds. 

 Upon the evidence derived from these memoirs and his own in- 

 vestigations of the fossils of the corresponding Hanoverian deposits, 

 M. Struckmann has constructed an elaboi-ate table showing the 

 horizons at which the common species, 125 in number, occur, and 

 the results of this table for the great classes of organisms he sum- 

 marizes as follows (see next page) : — 



The conclusions at which M. Struckmann arrives from the study 

 of this table are as follows] : — 



1. In all, the table shows 125 species of fossil remains of animals 

 which are common to the English and Hanoverian Upper Jurassic 

 series. Of these, nearly half (48 per cent.) belong to the Bivalve 

 Mollusca, 21 per cent, to the Gasteropods, 12 per cent, to the Echinoids, 

 6 "4 per cent, to the Cephalopods, and 4"8 per cent, to Corals. The 

 number of Cephalopoda is comparatively very small, a circumstance 

 due to the extraordinary poverty of the North -German Upper Jura, 

 and especially its upper portions, in remains of this class of animals. 

 On the other hand, the Echinoidea are comparatively strongly repre- 

 sented, which may be because, both in England and North Germany, 

 they have been within the Isat few years subjected to a thorough 

 monogra[»hic treatment, and are therefore better known than other 

 classes of animals. With regard to the Corals, I am convinced, says 

 M. Struckmann, that a considerably larger number of common species 

 will be recognized, as soon as the Corals of the North-German Upper 

 Jura have been worked out monographically. 



The table shows at once that the agreement of palaeontological 

 conditions is much greater in the lower part of the Upper Jurassic 

 formations than in the higher deposits, a phenomenon by no means of 

 isolated occurrence; for I have already shown ^ that the Oxfordian 



1 Quart. Journ. Geol. Soc. 1877, p. 260. 



2 Quart. Journ. Geol. Soc. 1875, p. 196. 



3 Quart. Journ. Geol. Soc. 1880, p. 180. 



* Der Obore Jura der Umg. von Hannover, p. 166. 



