T. Mellard Reacle — Oceanic Islands. 75 



17. Craven Arms, rotten limestone near the. 

 Spicules (%- and 6-rayed). 

 Conodoiits. 

 Pearls (?). 



The LagencB (mounted on one slide) from Lincoln Hill, the Railway-cutting at 

 Ironbridge, Dormington, Woolhope, and Benthall Edge, comprise: 

 Lagena vulgaris, Williamson, var, Icezns, Montagfu (with tubuliferous neck). 

 ,, ,, ,, ,, clavata, D'Orb. 



,, ,, ,, ,, sjilcata, Walker and Jacob. 



The close correspondence of the Eecent with these Silurian forms 

 is very noteworthy. 



The ]Dresence, also, of some Entomostracan species apparently 

 identical with Carboniferous forms is to be noted as an additional 

 example of recurrence (like the Silurian BeyricJiia intermedia in the 

 Cai'boniferous Limestone of Eussia). The presence, also, in these old 

 deposits oi Eiitomostraca indistinguishable, as to valves, from recent 

 genera, should not be lost sight of. 



I submitted Mr. Smith's Collection of Upper- Silurian Eiito- 

 mostraca to my friend Mr, J. W. Kirkby, and he favoured me with 

 the following remarks : — 



" With this I return you Mr. Smith's Silurian Entomostraca, which 

 I thank you for the sight of. They are the best Silurian specimens 

 that I have seen. Some of the Gijthere-Y\k(i forms appear to come 

 pretty near Carbonifei'ous species, as you pointed out to me. A set 

 on one slide can scarcely be distinguished from Miinster's Cythere 

 hilohata, and on other slides there are specimens that I suppose we 

 should have named G. cequcdis, J. and K., and C. obtusa, J. and K., 

 had they been found in Carboniferous strata." 



Y. — Oceanic Islands. 

 By T. Mellard Eeade, C.E., F.G.S. 



THE Pacific and Atlantic Oceans far from the continental masses 

 of land are studded with islands, which from their being solely 

 volcanic and of an age going back no further than the Tertiary 

 period, are considered to lend great support to the hypothesis of the 

 permanence of the great oceans and continents. Those who hold 

 these views question the right of New Zealand to be considered a 

 truly oceanic island, though on what grounds has never been quite 

 intelligible to me. Waiving this objection for the purpose of argu- 

 ment, I propose to discuss the bearings of the facts, as formulated by 

 those who believe in the " approximate " immutability of land and 

 sea. 



But before this can be done it will be necessary to consider the 

 vertical limits within which Dr. Darwin's generalization, that the 

 "great oceans are still mainly areas of subsidence, the great archi- 

 pelagoes still areas of oscillation of level, and the continents areas 

 of elevation," ^ coukl have acted. An approximate calculation tells 

 me that had one-half of the ocean floor subsided 1500 feet since 

 Cambrian times, the period Dr. Darwin adopts for the commence- 

 ment of this state of things, the then land, if it possessed the 

 1 Origin of Species, 4th edit. p. 373. 



