Mav io. iSg-t] 



NA TURE 



27 



ALPINE GEOLOGY. 



Ein Geologischcr Ouerschnitt diirch die Ost Alpen.—A 

 Geological Transverse Section through the Eastern 

 Alps.— By A. Rothpletz. (Stuttgart : Schweizerbart, 

 1894) 



1'"HE title of this work at once announces its impor- 

 tance in Alpine geology. Most of us, young and 

 old, are familiar with the section through the Eastern 

 Alps which we owe to the veteran Austrian geologist 

 Hofrath von Hauer. Since 1857, this section, from Passau 

 to Duino.has held its place alone in atlas and text-book. 

 In recent years, Swiss sections, more especially Helm's, 

 have been placed side by side with it, but they only em- 

 I brace the northern tlanks and a part of the central chain. 

 iDr. Rothpletz has given us in this volume the second 

 'complete section through the .Alpine chain. He has laid 

 ithe line of section farther east than von Hauer'5,begin- 

 Ining at the Bavarian plain in the north, and traversing 

 ithe Karwendel Mountains in the Bavarian Highlands 

 land North Tyrol, the Tuxer and Zillerthal Mountains, 

 east of the Brenner Pass, the Seisser Alpe, Schlern 

 Rosengarten and the Predazzo district in South Tyrol, 

 land the Sette Communi in the Italian Highlands. 



The section, which is printed with colours, extends 

 lover a surface area 140 miles in breadth, and has the 

 iadvantage of being drawn to true scale, vertical and 

 horizontal (i : 75000). So accustomed are we to exag- 

 gerated heights in Alpine sections, that this true-scale 

 section conveys an impression of rather unimposing 

 mountains and broad valleys. The eye misses also the 

 familiar dotted lines connecting detached parts of the 

 same geological strata, and helping one to a general 

 ,appreciation of the author's conception of the whole 

 '^ection. 



i The absence of any such lines is almost a key-note to 

 Ihe character of the work. In the text, the author de- 

 clares his opinion that (purposes of explanation, of 

 icourse, excepted) geological sections should represent 

 so far as possible only what has been actually observed, 

 and should not suggest, by means of dotted lines or con- 

 tinued bands of colour, what may be, after all, only 

 imaginary structural relations of the strata. The author's 

 jposition in this respect is made very clear in the chapter 

 on the " Glarner Double-Fold." 



The bulk of the text is devoted to descriptive, strati- 

 graphical, and tectonic details of the various districts 

 surveyed by the author along the line of section, and is 

 illustrated very fully by sketch-maps and sections. Rigid 

 Faithfulness of observation is a marked feature through- 

 out. The same care and precision which may be traced 

 in field-methods, has also been bestowed on the literary 

 workmanship of the book. The treatment of the Bavarian 

 Highlands is quite delightful. The drawings display so 

 anmiitakably the dependence of the main physical 

 features on the strata, and the contrasts of landscape 

 which tectonic disturbance has frequently produced. We 

 read with et[ual interest of the synclinal fold in which the 

 Walchen lake and the Jachenau valley now find them- 

 selves, and of the transverse faults which divert the 

 l.oisach and the Isar rivers out of their easterly course 



NO. 128c, VOL. 50] 



into a northern. On the other hand, in the case of the 

 bend of the Inn Valley at Worgl, it was a pre-Alpine 

 oligocene basin whose soft strata guided the river north- 

 ward to the Bavarian plain. Again, the author's powers 

 of exposition are seen to advantage when he demonstrates 

 the important fault-line between the Mesozoic limestones 

 north of the Inn and the old crystaUine rocks of the 

 central massif. He proves also beyond dispute the 

 geological independence of the Tu.xer and ZiUerthal 

 groups north and south of the Inner Pfitsch valley. But 

 we confess to a feeling of disappointment that although 

 the section passes through these groups, it has been able 

 to do so little to clear away the difficulties of the Central 

 Alps. Several important questions are discussed without 

 advancing us far— for example, the age of the granite 

 intrusion north of Brixen, the significance of the ser- 

 pentine rocks in the " Tarnthal Kopfe," the constant 

 occurrence of a rocklike "sernifit"at the unconformable 

 succession of Permian and Mesozoic strata on the old 

 Palaeozoic and crystalline floor. 



Strict adherence to the truths observed in nature, while 

 in itself laudable, seems somewhat to cramp boldness 

 and freedom of thought, and we are landed in a mist of 

 possibilities hovering over a conjectured Triassic period 

 of mountain movement in the Central Alps, which may 

 just as well have been post-Neocomian for all that is 

 proved to the contrary. A similar uncertainty envelops 

 the age-relationships of the overthrust at Tristkogl 

 (Karwendel Mountains), whose special misfortune it is to 

 be directed to the south, whereas the overfolding and 

 overthrusting elsewhere in the Northern Limestone Alps 

 are northward. It seems just possible that the over- 

 thrusts in this district are not all told.' 



One of the most striking chapters in the first part of 

 the book is that on the origin of the Schlern Dolomite in 

 South Tyrol. 



Part iii. leaves no doubt as to the author's conception 

 of the form of Alpine structure elucidated by his com- 

 plete section. In his ideas he difters considerably from 

 the recognised tenets either of Sue?s or of the Swiss 

 school represented by Heim. Dr. Rothpletz puts the 

 actual areal contraction due to late tertiary folding in the 

 Alps at a much lower figure than Heim did. He empha- 

 sises the importance of vertical faults and the great part 

 played by previous Alpine movements in determining 

 the occurrence of overthrusting and overfolding during 

 Pliocene pressure. He finds Suess' theory of the causes 

 of mountain-movement insufficient, and suggests that if 

 the earth's cooling resulted in radial expansion instead of 

 radial contraction, as Suess assumed, a quite as likely 

 explanation could be given of the actual facts observed 

 in crust-movements. 



Even if we cannot accept the dicta as final, we must 

 welcome the thoroughly scientific spirit in which the 

 author analyses the various doctrines, and shows what 

 part or parts are doctrines of faith only, and what of 

 the remaining are, in his experience, tenable or unten- 

 able. His own opinions are fixed upon most points, 

 but he never seeks to impose opinions on his reader ; 

 facts alone are taught ; and there is no more thirsiy soil 

 fjr facts than Alpine geology. 



M.\RI.\. M. LGILVIE. 



