GEOLOGY. 



By T. Sterry Hunt, LL. D., F. R. S. 



EOZOIO ROCKS. 



The question of the Eozoic or Primary rocks, details regarding which 

 were given in the report of last year, continues to occupy a prominent 

 place in geological literature. Giekie, the director of the geological 

 survey of Great Britain, has, in a late communication to the Geological 

 Society of London, attempted to set aside the conclusions arrived at by 

 the later British geologists, and to maintain that the great groups of 

 crystalline rocks which these observers have recognized as more or less 

 distinct pre-Cambrian series are either altered Cambrian strata or 

 erupted rocks of still later date. This conclusion, and the facts alleged 

 in support of his view are denied alike by Hicks, Hughes, Bonney, and 

 others, and we are promised an extended discussion and re-examination 

 of the subject, which, it may be predicted, will lead to the final refuta- 

 tion of the ideas of the old school, now defended only by the official 

 geologists, and the correlation of these crystalline rocks with those of 

 North America and of the Alps, now shown to be of pre-Cambrian age. 



In this connection it may be mentioned that the familiar doctrine of 

 the igneous and eruptive origin of the undoubtedly Eozoic, or pre-Cam- 

 brian rocks has been of late resuscitated by C. W. Hitchcock and by 

 Marr, among others. The latter, in an elaborate essay in the Geological 

 Magazine (June, 1S83), insists upon the supposed permanence of ocean- 

 basins, and the growth of continents from their borders, as now main- 

 tained by some geologists. Such a view presents great difficulties to 

 those who maintain the marine origin of Eozoic rocks, and Marr proposes 

 to regard them as of igneous and terrestrial origin; or, in other words, 

 as derived from materials ejected from volcanic vents, either in liquid 

 or in solid form, which by subsequent changes have given rise to the 

 granitoid gneisses and succeeding crystalline schists. This view, which 

 is by no means new, fails to account for the intercalation with these 

 stratified crystalline rocks of various special deposits, such as limestone, 

 apatite, iron-oxyds, quartz, metallic sulphides, and silicates like olivine, 

 serpentine, and pyroxene, all of which, in interstratified masses, form 

 integral parts of the oldeK crystalline series. These it is sought to ex- 

 plain as the result of local metasomatism. The hypothesis which sup- 

 poses them to have originated in an alteration of sediments like those of 

 later times is equally untenable without invoking metasomatism, and 



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