Professor T. G. Bonnet/ — Schists in Lcpontine Alps. 161 



boundary along a line joining Eas El Banul and Missikat El Qukli 

 ranges. This gneissose granite is especially conspicuous owing to 

 the abundance of the dykes of quartz-felsite and dolerite which vein 

 it, in a north-east and south-west direction, the differential weathering 

 of the two giving rise to a typical alternation of parallel ridges and 

 sandy valleys to which the name ' dyke-country ' may be applied. 

 Where the above two varieties come in contact, it can be clearly 

 seen that the red granite is the younger of the two. 



General Eecapitulation. 

 We are now in a position to give the general succession for the 

 Arabian Desert between Jebel Gharib and the Qena-Qosseir line. 



1. The metamorphic are older than the igneous rocks. 



2. The gneiss of Meeteg is the oldest member of the metamorphic 

 series, the schists coming next in order, followed by slates, grauwacko 

 (altered ash), sheai-ed diabases, and dolerites. 



3. Volcanic action had already begun during the period of 

 formation of the grauwackes and slates, as the sheared diabases and 

 dolerites are in places closely associated with them, but the main 

 mass of the dolerite is younger than the slates. Thus the next in 

 succession is a volcanic series in the south, consisting mainly of 

 dolerites and sheared diabases, and in the north of dolerites, 

 andesites, tuffs, and agglomerates. 



4. These are themselves underlain, and in most cases intruded 

 into, by a third series, a qiiariz-diorite or grey granite, in many 

 cases gneissose. 



5. Through the volcanics and grey granite rise masses of red 

 granite, which may be almost contemporaneous with dykes of quartz- 

 felsite and dolerite, seaming the members of the preceding series. 



IV. — Schists and Schistose Rocks in the Lepontink Alps: 



Reply to Criticisms by Professor A. Heim. 



By Professor T. G. Bonxey, D.Sc, LL.D., F.E.S. 



SOME three years ago, on referring to the twenty-fifth volume 

 of the "BeitrJige zur Geologischen Karte der Schweiz," I found 

 Professor Heim had devoted a few pages (pp. ol6-319) of that 

 work to my criticisms of his attempts to prove that Jurassic rocks 

 had been metamorphosed into schists containing authigenous garnets, 

 staurolites, etc. Had he brought forward any new fact of importance 

 or pointed out any serious error in my work I should have loplied 

 at once, but as he was unable to do this, and as the justice of one of 

 my criticisms was indirectly admitted in the petrographical appendix 

 by Dr. C. Schmidt, I allowed more pressing and interesting matters 

 to take precedence of one which had become chiefly personal. 



On reading Professor Heim's remarks I perceive that we labour 

 under a similar disadvantage, viz., that neither is a master of the 

 language in which the other writes. He complains of a difticulty 

 in understanding ray meaning, though I think it was plain enough 

 to most of my English friends. I am in the same position, l)ecause 

 he appears to me to avoid the direct issues and to repeat assertions 



DECADE lY.— VOL. VIII.— NO. IV. 



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