144 Reports amd Proceedings, 



which only took a secondary position as the builders of these rocks. 

 These animals included corals {Anthozoa), crinoids {Echinodermata), 

 bryozoa, sponges (AmorpJiozoa), Foramimfera, and amongst these the 

 Biatomacece also took an important position in eliminating the sili- 

 ceous matter held in solution ; but these were all animals which re- 

 quired clear water, free from sedimentary matter, in order to fulfil 

 their functions. 



Sedimentary strata on the other hand, being the detritus of land 

 surfaces carried down and deposited by currents over the floor of the 

 sea, could not co-exist in any quantity with the calcareous formations, 

 but must have had a source at some region opposite to the centre of 

 distribution of the limestones. Hence the conclusion was drawn — 

 (1). That in any natural group of rocks the calcareous and sedi- 

 mentary members must have had their sources in opposite centres 

 of dispersion; and (2). That the maximum development of these 

 two classes of strata must be at opposite points of a special region. 



The ''passage beds" and alternations of limestones with shales 

 and grits, similar to those of the lower carboniferous series in the 

 north of England, were accounted for on the ground of the alternate 

 predominance of the vital and mechanical conditions of marine 

 depositions over intermediate areas or border lands. 



The tendency of geological groups to arrange themselves in a 

 threefold order — the lowest and highest members being of sedi- 

 mentary materials, and the central one calcareous — was then alluded 

 to ; and the lecturer proposed a classification of this kind for the 

 whole of the geologic series, from the Lower Silurian to the Tertiary 

 inclusive, and believing this to be a truly natural grouping, he 

 accounted for it on the ground that each natural group was composed 

 of the representatives of three periods — the 1st, one of movement, 

 accompanied by change of land and sea and much denudation ; 2nd, 

 a period of comparative repose, and a minimum of denudation ; and, 

 3rd, of change, gradually increasing in intensity to the close of 

 the epoch. 



The following is a brief outline of the classification as proposed by 

 the lecturer : — 

 Tertiarv ( ^* ^^^i^^ntary — Miocene beds. 



p '-? \ 2. Calcareous — Nummulite Limestone. 

 ' 1. Sedimentary — Lower Eocene beds. 

 3. Sed. — Uncertain. 



2. Cal.— Chalk. 

 1. Sed. — Greensand and Gault. 



3. Sed. — Marine equivalents of the Purbeck and Wealden. 

 Portland. \ 2. Cal. — Limestone. 



1. Sed. — Sands. 

 Coralline ( l' ^^f-^^^^' 9^^* ^^^ Kimmeridge Clay. 

 Oolite. I Cal.-Corallme Oolite. 

 { 1. Sed.— Calc. Grit. 

 Lower \l' Sed.-Oxford Clay. 

 Jurassic ) ^^^* — ^^^^^ Oolite Limestones. 



V 1. Sed. — Lower, Middle, Upper Lias. 



Creta- 

 ceous. 



