ANNIYEESAEY ADDRESS OF THE PRESIDENT. XXXIX 



of a few types, and by the paucity or absenco of others — the maxi- 

 mum of murine life being about the top of the Scar Limestone, or 

 the base of the Yoredale Series. 



So in the Silurian series of the Malvern tracts, the maximum zone 

 of life is in the "Wenlock group, while from below (in the black 

 shales) the numbers of species rise from almost zero to 176, and then 

 dwindle again to zero in the Downton Sandstones, at the base of the 

 Old Ked. So in the Lias, the lowest beds yield very few shells, and 

 no Ammonites or Belomnites ; but from this the numbers Swell 

 rapidly to a maximum, which for many groups is in the Oolitic series 

 of Lath (but for Ammonites and Lelemnitcs is in tho Lias), and 

 decays to a minimum in the comparatively poor Oolites of Portland, 

 Swindon, and Aylesbury. 



In the Cretaceous strata we may perceive very clearly tho influ- 

 ence of physical conditions on tho zones of greatest fertility; for 

 while the Mollusca generally are more abundant in the Grecnsands 

 and Gault, the Amorphozoa, Foraminifera, and Lryozoa seem moro to 

 affect the Chalk, and specially the Upper Chalk, from which most of 

 the Ammonites have disappeared. Fishes are most plentiful in the 

 Upper Chalk. 



Nor can we fail, whilst studying tho distribution of the Cretaceous 

 fauna, to perceive a distinction of north and south districts, if not 

 provinces, within the limits of Lritain. The northern chalk of York- 

 shire is comparatively poor in fossils, and, instead of tho Belemnitella 

 .inuruiiiihi, so common in the south, gives us in abundance Behm- 

 nitetla quadratd, which the chalk of the Laltic exchanges for B. 

 tnammiUata. Observations of this kind, well carried out, appear to 

 justify the belief that in different or only occasionally connected 

 banns the succession of forms might be somewhat different; and 

 that groups might be analytically resolved into several stages in one 

 1 Pad , united together in a second, or complicated with new auxiliaries 

 in a third. 



The two most contiasted provinces of the middle Palaeozoic strata 

 (the Devonian and Welsh tracts) 0&et, in regard to their forms of 



life, a very marked difference: little hut Fishes in the latter: abun- 

 dance of ntollusCU, Trilobitee, Zoophyta, and Lryozoa in the former. 

 The tatter is b tract of mostly peroxidated sediments; tb.0 Jbnner 

 lias a large proportion of protoxidated rooks, and is these principally 

 are the treasures of fossil Life. Bediments brought in different direo* 



ticiis. with germs of lOCal groups Of contemporaneous life, are indi- 

 cative of these facts, which, besides, suggest to us the necessity of 

 reconsidering with care the relation of the truly limited Devonian 

 to the greatly expanded Carboniferous and Silurian strata. 



In the case j u - 1 mentioned, then, there is often traceable a DOB* 



currence andcoextension of certain gives fossils with certain mineral 

 deposits tin' fossils coextensive with and limited to those particular 

 deposits. So al.~o the deposll ofAymestry Cimestose is the favourite 



home of the COnSpicUOUS /'< nliirm n>s hni'/lilii, -which maV he looked 

 for in vain where the limestone dies out in contemporaneous muddy 

 shales. "When the Uradford Clay disappears, the peculiar local fauna 



