AJTNITERSARY ADDRESS OF TI1E PRESIDENT, xli 



of the English Coal-measures with the Magncsian Limestone series, 

 which generally show remarkable unconformity, but in a tract of 

 Yorkshire arc nearly or perhaps quite conformable. Here the exact 

 nature of the mineral changes, and the zones of Axinus, Stropha- 

 losia, Nautili, Mytili, and other shells, will become better known by 

 the progress of the Geological Survey, which is now extended to that 

 region. 



I may also refer to the still unsettled questions regarding the 

 triassic or liassic affinities of the bone-bed and the lowest Lias 

 shales, sands, and calcareous layers, — on which a valuable communi- 

 cation has reached us from Dr. Wright. This active palaeontologist 

 is proceeding with his careful survey of the several divisions of the 

 Lias in the south of England, and accumulating data for the further 

 discussion of the boundary (if it be necessary to draw as a line what 

 nature marks as a zone) between the Upper Lias and the Inferior 

 Oolite. 



§ Distribution of Ammonites. 



Throughout the Lias and the whole Oolitic system, the evidence 

 of Ammonites is acknowledged by all geologists to be of the highest 

 value in determining the place of detached deposits on the general 

 scale of ancient life and time. This arises in a great degree from the 

 circumstances that the whole group of true Ammonites is limited in 

 time between the Trias and the Tertiaries, and that the species are 

 very numerous, very definitely marked, traceable from youth to age, 

 and grouped naturally into distinct assemblages, whose place in the 

 succession is constant. On these grounds Dr. "Wright may well 

 be justified in attaching to them the same importance which was 

 assigned to them by W. Smith, whose unpublished Table of the 

 Distribution of Ammonites, drawn up by my own hands in 1817, is 

 now laid before the Meeting. It forms one of a scries of such 

 attempts, of which an example has been printed, viz. the Table of 

 Echini, in the ' Stratigraphical System of Organized Fossils' (1817). 

 Von Bach's valuable labours on the Ammonitida: are well known. 



There yet remain a few unsettled points of classification of the 

 English and Scottish Btrata of the Oolitic series, for which a precise 

 knowledge of the sequence of Anunonitic forms may furnish a clear 

 explanation. Dr. Wright has lately placed before the Society a 

 proposal to assign to the Inferior Oolite of Yorkshire a portion of 



the sandy, shaly, irony and calcareous beds which Prof, Morris and 

 myself have r efer red tO the oolite of Lincolnshire, which at proeia 



stands for the representative of the Great Oolite of Hath. The 

 evidence of fossils appeared even in 1826 L828 in favour of refer- 

 ring these oolites of < iave and ( Iristhorpe to the I oferior I lolite ; but 

 it seemed indecisive to jnr, and has appeared so to almost every 

 subsequent inquirer. In the Bectiou referred to, between onequi- 

 Vocal Lias and onequivoca] Cornbrash there have been gathered very 



few Ammonites in addition to what were mentioned in my volume. 



In addition to Asmtnwnites Blagdeni, which was found at Gristhorpe 

 so long ago, the diligent naturalists oi Scarborough have collected 



VOL. \\ I. ll 



