316 A. J. Jukes-Browne — On the term Neocomian. 



It is now time to examine the succession exhibited in our southern 

 counties, where, as is well known, the series consists of a thick mass 

 of freshwater strata (Wealden beds), overlain by marine clays and 

 sands which are known under the name of Lower Greensand. These 

 marine beds are everywhere divisible into three stages, the fossils of 

 which are to a certain degree different. In the Wealden area there 

 are : — 



3. Folkestone and Sandgate beds, with Bhynchonella Gibbsii, Eli. 

 sulcata, Thetis Sowerbyi, Corbida elegans, etc. (150 feet). 



2. Hythe beds, with Plicatula placunea, Exogyra sinuata, Ammo- 

 nites Martini, Am. furcatus, Ancyloceras gigas, A. Hillsii (200 feet). 



1. Atherfield Clay, with Trigonia caudata, Tr. dcedalea, Perna 

 Mulleti, Holocystis elegans, etc. (90 feet). 



In the Isle of Wight the corresponding series is very much thicker, 

 but may be divided as below : — 



3. Shanklin Sand, sands and clays down to the sand with ferru- 

 ginous concretions (256 feet). 



2. Walpen Sands and Crioceras beds, with Am. Martini, Ancijlo- 

 ceras gigas, An. Hillsii, Exogyra sinuata, and Ter. sella (400 feet). 



1. Atherfield Beds, with Trigonia caudata, T. dcedalea, Perna 

 Midleti, Gorbis corrugata, and Aporrhais Eobinaldina (150 feet). 



Now as the Atherfield Clay is certainly not older than the Khoda- 

 nien of Eenevier, there can be little doubt that the two higher groups 

 form an expanded equivalent of the French and Swiss Aptien. The 

 Urgonian facies of the Atherfield fauna was recognized long ago 

 by M. Cornuel, but he remarks in 1874 that " no clear separation 

 between the Neocomien (i.e. Urgonien) and Aptien can be traced in 

 the Isle of Wight, on account of the mixed assemblage that occurs 

 in the Crackers, which form a passage from one to the other." 1 It 

 is evident therefore that here, as in the south of France, there is a 

 complete passage between the representatives of the Urgonien and 

 the Aptien. 



It is only necessary to add that the lower marine beds have a 

 limited extension, and that the uppermost beds (Shanklin sands) 

 overlap them and spread northward over the Jurassic rocks, all the 

 so-called Lower Greensand of our midland counties belonging to 

 this group, the range of which is probably continuous beneath the 

 Gault as far as Norfolk, where they pass into the upper beds of the 

 northern Cretaceous area. 



In Lincolnshire and Yorkshire beds older than the Aptien once 

 more make their appearance, and in this area we appear to have a 

 much more complete marine series than that of the southern counties. 

 The Yorkshire succession has been well described by Prof. Judd 

 some twenty years ago, and descriptions of the Lincolnshire beds 

 will shortly appear in the Memoirs of the Geological Survey. The 

 grouping adopted by Prof. Judd, however, does not appear to be 

 entirely satisfactory, and his correlations with Neocomien, Urgonien, 

 and Aptien have not been accepted by French authorities, so that I 



1 Bull. Soc. Geol. de Fiance, 1874, p. 390. 



