Dr. Irving — On the Airolo Schkts. 253 



geological students may be pretty much that of the Bavarian 

 veteran. 1 It is with the hope of thi-owing a little light on the 

 subject that the present writer has put pen to paper. For it is not 

 too much to say that the subject is one of critical importance. 



The appearance of Dr. Heim's great work 2 on the Todi-Wind- 

 giillen Group of the Central Alps marked almost a new departure in 

 the investigation of the forces employed by nature in mountain- 

 building. In some of his theoretical views drawn from the facts 

 described in that work Heim had been anticipated by Prof. Suess of 

 Vienna, 3 and the priority is generously acknowledged. The work is 

 well known ; but the student needs to be warned against the false 

 inferences on some points which he will probably draw from the 

 sectional descriptions in the Atlas, if he omits to study the cor- 

 responding portions of the text of the work. If anything could 

 exceed our admiration for this splendid contribution to physical 

 geology, it might be that which we all felt for the magnificent 

 series of transverse sections of the Alps — the work of Prof. Heim 

 and his pupils at Zurich — exhibited in the temporary Museum 

 of the International Geological Congress at Burlington Gardens in 

 September, 1888. In his recent little work 4 the present writer has 

 discussed many of the facts furnished by Dr. Heim in their bearing 

 upon questions connected with the metamorphism of rocks. In his 

 Essay on the Crystalline Schists, 5 in 1888, Heim indicates clearly 

 the extent to which he is prepared to go in applying the principles 

 of ' dynamo-metamorphism.' He expressly warns geologists against 

 rash generalizations in the direction of " regional pressure-metamor- 

 phism," from the exceptional and abnormal structural facies pre- 

 sented by those Alpine masses, which he knows most intimately, and 

 has described in such a masterly way in his great work. It is 

 unnecessary to occupy space here with quotations, since a translation 

 of Dr. Heim's essay has been published. 6 



Dr. Heim's letter, a translation of which was read by Dr. Geikie 

 at the meeting of the Geological Society on the 22nd of January, 

 1890, seemed to contain little but what those who had made a study 

 of his great work were familiar with before. But if it served no 

 other purpose, the publication of that letter is most opportune as 

 a reply to some remarks in a recent Number of the Geological 

 Magazine. 7 J. J. H. T. may learn from it that, by the Swiss geologists 

 at least, the " primitive crust of the earth " is not by any means 

 regarded as a "geological Will o' the wisp." Dr. Heim's own 



1 " It was the English," Kaspar cried, 

 ' ' Who put the French to rout ; 

 But what they fought each other for, 

 I could not well make out." 



2 Untersuchungen uber den Mechanismus der Gebirgsbildung. 



3 Die Entstehung der A /pen, a work of great value and interest. 



4 Chemical and Physical Studies in the Metamorphism of Rocks (London, 1889). 



5 See Etudes stir les Schistes Crystallins, published by the International Geological 

 Congress (London, 1888). 



6 See Nature, vol. xxxviii. Sept. 27, 1888. , 



7 Decade III. Vol. VII. (January, 1890), p. 36. Prof, de Lapparent's V Ecorce 

 Terrestre (Brussels, 1888) is worthy of consideration. 



