XXXViii PROCEEDINGS OE THE GEOLOGICAL SOCIETY. 



§ Zones bf Life. 



To complete our knowledge of a geological province, we should 

 remember that, as in dredging the sea-bed account is taken of the 

 depth of water, the force of currents, and the quality of ground, so 

 in geological investigations of precision we should expect similar 

 attention to the separate collections from the coarse sands and 

 pebbles of the shore, the drift sands, the muddy expansions, and the 

 calcareous rocks. The general results to which we are accustomed, 

 which sum the whole into one catalogue for a given period, furnish 

 no doubt, the best means of contemplating the system of life of the 

 period ; but in local monographs, and in monographs of species o 

 groups, the exact distinctive characters of the repository should, a s 

 far as possible, be recorded. In regard to depth of water, it is only 

 by the record left in the structure of the stone, and succession of 

 laminas, that we can find an independent measure ; and in this Mr. 

 Sorby has greatly helped us. A measure of depth derived from the 

 •analogy of the fossil to the recent groups is seldom to be implicitly 

 trusted. We may remark, further, that a series of fossils for any 

 system, to be complete, should include three groups — from calcareous, 

 arenaceous, and argillaceous repositories ; for these three sets of 

 deposits are really contained in each natural system of strata. One 

 of the earliest and most profitable exercises of my life was the 

 making a catalogue of the fossils in the collection of W. Smith, 

 before the removal of it to the British Museum. "When I had, follow- 

 ing my great relative's guidance, enumerated the 720 species of fossils 

 in. his collection, he set me to compose those tabular synopses of the 

 distribution of the more remarkable groups of fossils in the several 

 zones of stratification of which the Table of Echinodermata in the 

 < Stratigraphical System of Organized Fossils ' (1817) is an example. 

 No sooner were these constructed for a few groups, than two ideas 

 were strongly imprinted on my mind : — 



1. That the groups of fossils had some real relation to the mineral 

 and structural characters of deposits ; so that, while smooth oysters, 

 Gryphwce, &c, were frequent in clays, and Terebratulidae rare in 

 them, we were to look for Zoophyta and Echinodermata in the cal- 

 careous bands ; Spongiadae in some sands and some particular lime- 

 stones; few fossils of any sort in peroxidated sediments, coarse 

 conglomerates, or pure sands of any colour. It appears to me that 

 this class of inquiry is still not enough followed out, either by ex- 

 plorers in local districts or by the palaeontologist of the study. With 

 so much the more pleasure, therefore, I welcome the extended ex- 

 ample of such studies given by Dr. Bigsby in his comparison of the 

 Silurian Eauna of North America and Europe. 



2. That in each great natural zone of fossils there was to be traced 

 a poor origin, a rich development, and a subsequent decrease, — thus 

 apparently giving to each great natural period a zone of maximum 

 fertility in species, in which, more than at any other time, the 

 various orders of life acquire their full expression. With this idea 

 in his mind, a palaeontologist finds the whole Carboniferous period 

 one, though in it are several zones distinguishable by the prevalence 



