THE ARCHJEAN ROCKS M 



(2) finer gneisses and mica-schists, often traversed by dykes of 

 serpentine and epidiorite, and finally a series (3) of micaceous, 

 calcareous, and chloritic schists, between which and the older schists 

 there is a marked lithological difference and contrast. 



Recently, however, grave doubts have been thrown upon the 

 view that these are all Arcluean rocks, upon the age of the gneiss 

 by Professor J. W. Gregory, 83 and upon that of the tchitUt luttret 

 by Kilian and Parona. Professor Gregory admits the apparent 

 sequence, but fails to find anything like a continuous band of 

 " central gneiss " as represented on certain maps ; only independent 

 isolated masses of gneiss which appear to be intrusive granites of 

 very recent date. Monsieur Parona, again, has discovered layers of 

 chert containing Radiolaria in the silvery schists, and the generic 

 assemblage suggests a Carboniferous or even Mesozoic age. 



Professor Gregory has specially studied the gneisses of the 

 Cottian Alps and finds that there is clear evidence of contact- 

 metamorphism both in the gneisses and the adjoining schists ; that 

 the gneisses invade different parts of the schist series with trans- 

 gressive junctions ; that they include large blocks of the schists and 

 serpentines ; that the schists are occasionally traversed by dykes of 

 aplite which appear to be apophyses of the gneisaic granite, while 

 the latter is not itself cut by any of the later igneous rocks. 



He concludes that the gneiss is really a granite of Pliocene date 

 and that the silvery schists are mainly Palaeozoic and probably of 

 Carboniferous age. Thus if these views are correct the only 

 Archaean rocks in the Cottian, and indeed in all the Western and 

 Italian Alps, are the series of mica-schists and calc-schista into 

 which the Tertiary granite has been injected. 



3. Bohemia 



Another large area of Archaean rocks is exposed in Bohemia and 

 Saxony, extending from the valley of the Danube on the south 

 through the Bohemian Highlands (Bolimer Wald) and the Erxge- 

 birge, and as far as Chemnitz and Dresden on the north, while 

 eastward it ranges into Moravia. In the northern part of this 

 region there is a basin of Palaeozoic strata extending from Pilsen 

 to Prague, and on the border of this the highest Arcluuan rocks 

 can be seen to pass below the Cambrian strata. 



The Archaean rocks of this region seem to resemble those of tin- 

 Eastern Alps, and a similar threefold division of them has been 

 made, those supposed to be the oldest consisting of gneisses much 

 interpenetrated by granites. In apparent succession to these are 

 mica-schists and phyllites, with intercalations of araphibolites, 



