THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE II. VOL. Vill. 



No. VII.— JULY, 1881. 



I, — Note in Explanation of Plate VIL, to Illustrate the 

 Theory of Subsidence and Elevation of Land, and the 

 Permanence of Oceans.^ 



By J. S. Gardner, F.G.S. 



Fig. 1 is intended to represent a section across an ocean basin. It 

 is supposed that the combined weight of water (1) and sediment (2), 

 acting upon an elastic layer of rock (3), compresses the fluid layer 

 which underlies it (4), and forces it to escape laterally, and either to 

 accumulate and partially solidify, thus raising the crust above ; or, 

 where the tension is extreme, and the resistance inadequate, to form 

 fissures or vents. The continuously sustained pressure towards the 

 centre of the basin constantly converts fresh solid into fluid, which 

 escapes again and again, perhaps at intervals of centuries, causing 

 fresh upheavals or eruptions, perpetually deepening the ocean basin. 



The relative mass of sediment to crystalline rock may be enor- 

 mously greater, since its accumulation must have been increasing 

 from the remotest ages. 



Fig. 2 represents the basin of the Pacific with its encircling chain 

 of volcanos, and is after Scrope. 



Fig. 3 is an ideal section similar to that of Fig. 1 ; but showing in 

 addition sub-marine lines of insufficient resistance. 



In the article, reference to one of the most striking examples of 

 subsidence being directly due to weight of sediment was omitted. 



The constant influx of brackish water seen in our coal-fields, and 

 the nature of coal, show beyond doubt that it was deposited at or 

 about the sea-level, yet in the South Wales district the Coal-measures 

 are 10,000 to 12,000 feet thick, with 75 distinct seams. 



II. — On the Genera Mjerista, Suess, 1851, and Ba.yia, Dav. 1881. 

 By Thomas Davidson, F.R.S., etc., etc. 



IN his memoir " Brachiop. der Kossener Schichten," p. 17, Prof. 

 E. Suess proposed his genus Merista, giving as its type the M. 

 Herculea, Barrande, and at page 85 of the German edition of the 

 general introduction to my work on British Fossil Brachiopoda Prof. 

 E. Suess redescribes his genus, and in pi. iii. figures its spirals and 

 shoe-lifter process ; but neither the connexions of the spirals, nor 

 their attachments to the hinge-plate, had then been discovered. 

 Prof. Suess also includes in his genus Merista the so-called Atrypa 

 tumida, Dalman (now the type of our genus Whitfieldia) , whose 



^ This Plate should have accompanied Mr. Gardner's article which appeared iu the 

 June Number, see pp. 241-245. — Edit. Geol. Mag. 



DECADE II. — VOL. VIII. — NO. VII. 19 



