1'62 Professor T. 0. Bonney — Schists in Lepontine Alps. 



whicla I have challenged. So, before going further, I will state the 

 dispute as clearly and concisely as I can. It arose out of a paper 

 read at the London Meeting of the International Geological Congress 

 in 1888.^ Then, or soon afterwards, Professor Heim made the 

 following assertions : (1) that at Guttannen stems of a plant of 

 Carboniferous age had been found in a gneiss ; (2) that near 

 Andermatt a crystalline marble was associated with a Jurassic 

 limestone, so that they must be of the same geological age ; (3) 

 that in the Lepontine Alps a transition could be traced between 

 fossiliferous Jurassic rocks and schists with authigenous garnets, 

 staurolites, etc. 



I have disputed the accuracy of all these statements. As regards 



(1) it is now admitted that the supposed stems are not organisms, 

 but merely imitative markings. Hence this assertion is invalidated, 

 but, as I have apparently made a mistake as to the nature of the 

 rock, neither side in this controversy can ' score honours.'^ About 



(2) there is nothing fresh to be said. I have discussed Prof. Heim's 

 evidence, which he has not been able to strengthen, and think 

 myself justified in claiming a verdict of 'not proven,' even if I have 

 not shown his interpretation to be improbable. ^ My remarks 

 accordingly will be confined to (3). Here sections are more 

 numerous ; the issue is simpler, and the initial difference between 

 us largely concerns matters of fact. In the first place, Prof. Heim 

 maintains that I have misunderstood him, and that he never affirmed 

 those altered Mesozoic sedimentary rocks to be true crystalline 

 schists. The very lax use of the term ' schist ' by Continental and 

 some English authors undoubtedly leads to confusion in expression 

 as well as in thought, and I am prepared to admit that it might some- 

 times be difficult to draw a hard and fast line between a schistose 

 rock (i.e. cleavage followed by a certain amount of secondai-y 

 mineral development) and some foliated schists. This, however, 

 does not really affect the present issue. Professor Heiru asserted 

 that certain schists with authigenous garnets, staurolites, etc., were 

 proved to be of Jurassic age, not only by stratigraphical evidence, 

 but also, where the minerals were less well developed, by the 

 presence of fossils. I asserted that the schists with garnets, etc., 

 were both truly crystalline and belonged to a group distinct from 

 the Jurassic rocks in question ; that this group could be shown to 

 be much older than the Trias, and to differ in important respects 

 from the fossiliferous schistose Jurassic rocks, which never contain 

 authigenous garnets, etc., but only certain hydrous silicates, pre- 

 senting a merely superficial resemblance to garnets, staurolites, etc. 

 In other words, I gave reasons to show that Professor Heim's 

 interpretation of the stratigraphical facts was untenable, and his 

 identification of the important minerals was incorrect. 



^ Compte Rendu de la 4"^ Session, p. 80. See also Nature, Sept. 27 and Oct. 4, 

 1888, and Quart. Journ. Geol. Soc, vol. xlvi (1890), p. 236. 



* Geol. Mag., 1900, p. 215. 



3 Quart. Journ. Geol. Soc, vol. xlvi (1890), p. 67 ; vol. 1 (1894), p. 285 ; vol. liii 

 (1897), p. 16. 



