6 2 SCIENCE PROGRESS. 



such terms as " metamorphosed slates," "siliceous slates," 

 "ribbon jasper," "chert," etc., have been applied by field- 

 geologists to wide extents of old volcanic rocks. Many of 

 these are of pre-Cambrian age (Huronian, etc.), but others 

 occur at various horizons among the Palaeozoic strata. From 

 so large a field it is to be anticipated that valuable informa- 

 tion will be forthcoming in the near future. 



Researches in various parts of America have also done 

 something towards filling the gap in point of time between 

 Palaeozoic and Tertiary igneous rocks. Indeed even in 

 Europe this gap seems to have been somewhat exagger- 

 ated. Both intrusive and volcanic rocks of Triassic aee 

 are known in the Tyrol, in the French Alps, etc. Others 

 of Cretaceous age occur in Portugal, in Moravia, Silesia, 

 Galicia, and the Russian province Wolhynia, and in the 

 Crimea. Some of these are of peculiar characters ; others 

 have been described by Lagorio under such names as 

 mesodacite, mesobasalt, etc., and differ in no essential from 

 their younger equivalents. According to Reyer and others, 

 forerunners of the Tertiary trachytic eruptions appeared in 

 the Euganean area as far back as the Upper Jurassic 

 period. Such facts have, of course, been appreciated by 

 many continental geologists, and when such influential 

 leaders as Rosenbusch consent to abandon the aee-criterion 

 in the classification of rocks and revise their petrographical 

 nomenclature accordingly, a serious obstacle to the progress 

 of petrology will have been removed. 



i 

 BIBLIOGRAPHY. 



(i) K. von Chrustchoff. Ueber ein palaozoisches Leucitges- 

 tein. Neu. Jahrb. fur Min., 1891, vol. ii., pp. 224-227. 



(2) SIR ARCHIBALD GEIKIE. [Review of Vulcanicity in the 



British Isles.] Presidential Addresses to the Geological 

 Society, 1891, 1892. Quart. Joum. Geo/. Soc, vols, xlvii., 

 xlviii., Proceedings. 



(3) Frederick H. Hatch. The Lower Carboniferous Volcanic 



Rocks of East Lothian (Garlton Hills). Trans. Roy. Soc. 

 Edin., vol. xxxvii., pp. 1 15-126, 1892. A new British 

 Phonolite. Geo/. Mag., 1892, pp. 149, 150. 



