200 Sir A. Geikie — Lamarck and Playfair — 



(a proposition so well enforced by Lamarck), and be continued to 

 invoke the action of subterranean beat, amounting sometimes to tbe 

 point of fusion, even for sucb deposits as rock-salt. 



Anotber serious defect in tbe Huttonian tbeory was strenuously 

 upbeld by its illustrator. Hutton bad done good service by insisting 

 upon tbe igneous and intrusive nature of many rocks in tbe crust 

 of tbe eartb, tbougb some of tbe evidence on wbicb be relied was 

 fallacious. Having convinced bimself tbat tbe sparry structure of 

 limestone and otber rocks and minerals points to tbe action of great 

 beat witbin the terrestrial crust under so vast a pressure as to 

 prevent tbe escape of tbe carbonic acid of tbe carbonates, be inferred 

 tbat tbe kernels of zeolite, calcite, and cbalcedony in tbe cavities of 

 amygdaloids are a proof tbat tbese rocks bave been injected in 

 a molten condition into tbe crust, and never reacbed tbe surface. 

 Playfair called tbem ' unerupted lavas,' and believed tbem to be 

 distinguisbable from superficial or truly * erupted lavas ' by tbeir 

 enclosed kernels of calcite and otber minei'als, wbicb are absent from 

 lavas poured out at tbe surface. He would not admit tbat any of 

 tbese older masses could be true superficial lavas wbicb migbt bave 

 been discharged over tbe sea-bottom and buried under later marine 

 sediments. He quoted, only to reject, tbe just observation of 

 Spallanzani tbat the amygdaloids of the Euganean Hills are true 

 superficially ejected lavas, tbe steam cavities of wbicb bave been 

 filled with minerals deposited by infiltrating water (§ 234). He 

 was evidently much impressed by tbe singularly interesting and 

 suggestive account given by Dolomieu of tbe intercalation of 

 successive sheets of lava among tbe limestones of Sicily, but be 

 would not admit tbat these lavas were poured out over the sea- 

 bottom as " imagined " by Dolomieu. He did not see tbat by 

 admitting tbe probability of ancient " submarine volcanoes " be 

 would in no way bave invalidated tbe proofs of intrusion demon- 

 strated by Hutton, but would bave obtained a new argument in 

 favour of bis master's doctrine of tbe continuity and antiquity of 

 Nature's operations (§§ 242-24i). 



To Playfair belongs the merit of having first exposed the gross 

 error of those Neptunists who, in support of tbeir opinion tbat 

 basalt is a rock which was deposited from solution in water, cited the 

 basalt of Port Rush in the north of Ireland as containing fossil 

 shells. His practised eye soon detected tbe source of tbe blunder, 

 a dark shale containing ammonites having been mistaken for tbe 

 basalt wbicb bad invaded and greatly indurated it.' 



One of the most memorable " Notes " to tbe " Illustrations of the 

 Huttonian Tbeory " is that in wbicb the author, discussing the 

 causes of tbe apparent changes in tbe level of the sea, maintains 

 that on the whole it is tbe land wbicb rises or sinks, and not the 

 surface of tbe sea (Note xxi). It would be difiicult to exaggerate 

 tbe importance of this contribution to geological literature. Although 



1 Playfair' s examination of the specimens from Port Push was made in company 

 with Lord "Webb Sejmour and Sir James Hall ("Illustrations," § 253). 



