294 



NATURE 



[January 24. 1901 



AN ALPINE CRUST-BASIN 



1 : Das geotektonische Problon der G lamer Alpen. A. 



Rothpletz. Pp. vii + 251, and Atlas. (Jena: Fischer, 

 1898.) 



2 : Geologische Alpenfors'chwigen. A. Rothpletz. I. 

 Pp. viii + 176. (Munich; J. Lindauersche, 1900.) 



A MORE than ordinary interest attaches to these two 

 works by Prof. Rothpletz, as they treat of the 

 boundary district between the Eastern and Western 

 Alps. This district is already famous in geology, and 

 has attracted all comers by its problems. My own 

 opinion regarding its structure had been formed while 

 I wrote my paper on the "Torsion- structure of the 

 Dolomites" in 1898, and was given by me at the British 

 Association Meeting and at the International Geo- 

 graphical Congress in 1899. I then compared the struc- 

 ture of this district with that of the areas of inthrow of 

 various sizes that I had studied in the Dolomites. I 

 described the Glarus-Prattigau area as a local area of 

 depression or crust-basin within the Alps, around which 

 fold-arcs had formed peripherally. Thrust-masses, taking 

 origin in the peripheral arches, had moved towards the 

 centre of the basin. And as across this area of depres- 

 sion the Alpine wave-movement of compression had also 

 passed, the leading strike-curve of the Alps had been 

 superinduced upon the local curves, making various 

 angles with those, so that the actual crust-forms now 

 presented to us were resultant combinations of the local 

 movements round the subordinate basin, with the more 

 extended Alpine movements round the North Italian 

 crust-basins. 



Our knowledge of the geology of this district has been 

 vastly extended by Prof. Rothpletz. The actual observa- 

 tions recorded in these works, the discovery of many 

 leading fossils in rocks whose age had hitherto remained 

 doubtful or been erroneously determined, the large 

 number of geological sections and the geological maps, 

 must be regarded as one of the most brilliant achieve- 

 ments in Alpine geology. Two gems of detailed geo- 

 logical mapping may be recommended for careful study, 

 namely, the north-west part of the Glarus district and 

 the fault-blocks of the Rhatikon : (i : Taf. xi., and 

 pp. 166-185 ; 2 : Taf. i., and pp. 69-90.) 



In all the leading text-books, the plication of the Alps 

 is referred to lateral compression having acted mainly 

 from the south in the Eastern Alps and rather more from 

 south-east in the Western Alps, hence the curvature of 

 the Alpine strike. Overthrusts are said to have taken 

 place chiefly towards the north on the north side of the 

 central chain, and towards the south on the south side. 

 Glarus, on the north of the central chain, offered an 

 exception to this rule, as according to Prof. Heim's epoch- 

 making work (" Mechanismus der Gebirge," 1878) there 

 had been within Glarus the advance of overthrust masses 

 both from the north and from the south during the last 

 Alpine upheaval. 



Prof. Rothpletz contended (i) the existence of an over- 

 thrust mass in the south of Glarus, and (2) the correctness 

 of Prof. Heim's conception of a crushed " middle-limb," 

 as theoretically necessary in the process of overthrusting 

 Prof. Rothpletz advocated that the phenomena of over- 

 thrusts were akin to differential movements between 



NO. 163c, VOL. 63] 



fault-blocks ("Querschnitt durch die Ost-Alpen," 1894, 

 and "Geotektonische Probleme," 1895). Prof. Rothpletz, 

 in his latest work on Glarus, in 1898, recognises the pres- 

 ence of a thrust-mass in the south of the Glarus area, but 

 treats it as a mass originally continuous with the large 

 thrust-mass on the north (<;/ p. 211), and concludes from 

 his observations that the whole of this " Glarus thrust- 

 mass" had travelled from east to west, a distance of 

 about twenty-five miles from the Rhine valley to the 

 Linth. The rocks that form the base of the thrust-plane 

 comprise all the geological horizons from the older gneiss 

 to Oligocene strata, and have been folded along a curved 

 strike, east-west near the Linth Valley, but curving 

 round a southern arc to N.E.-S.W. direction nearer the 

 Rhine Valley. 



In the south or " Vorderrhein " portion of the " Glarus 

 thrust-mass " the prevailing strike is N.E.-S.W. In the 

 northern portion the rocks of the thrust-mass are folded 

 along a curved strike, curving from S.S.W.-N.N.E. in 

 the vicinity of the Linth Valley round a northern arc to 

 an east-west strike. 



In both the basal mass and the overthrust mass the 

 folds have been overcast to the north and north-west, the 

 compression of the folds having been very much stronger 

 in the south than in the north. As many as ten folds 

 overlie one another in the basal mass at Brigelser Horn, 

 and are surmounted by a twisted portion of the thrust- 

 mass with strike veering from S.W.-N.E. to S.N. This 

 curvature is explained by Prof. Rothpletz as probably due 

 to the local resistance offered by two eruptive masses 

 (p. 160). 



Three higher tiers of thrust-masses are present on the 

 west of the Linth Valley in the Glarnisch Mountain ; two 

 of these thrust-masses continue in curved direction north- 

 eastward to the Schild Mountain and Lake Walen. The 

 names given to them by Prof. Rothpletz are the Schild, 

 Urner and Schwyz thrust-masses. Prof. Rothpletz says 

 these masses have travelled from the north-west, but he 

 expressly states his opinion that they advanced subse- 

 quently to one another and subsequently to the advance 

 of the Glarus mass from the east, or locally south-east 

 (p. 216). 



Looking now at the second work, which treats of the 

 east side of the Rhine Valley, the most important result 

 is the description of a Rhatikon and Silvretta overthrust 

 from the east. Prof. Rothpletz proves that the rocks of 

 the Rhatikon Chain rest on a basal mass which is the 

 natural continuation of the Glarus thrust-mass eastward, 

 and he concludes that the Rhatikon mountain mass 

 travelled from the Montafon Valley to the Rhine Valley, 

 about nineteen miles from east to west. Tracing the 

 origin of this thrust southward, he finds the rocks of the 

 Silvretta Massive have been thrust eastward above the 

 basal mass of the Prattigau, and still farther south the 

 overthrusts are continued in the Lenz and Oberhalbstein 

 mountain-group. The independence of the over-thrusting 

 and the folding processes may, in Prof. Rothpletz's 

 opinion, be concluded from the fact that the direction 

 which has been followed by the thrust-mass frequently 

 makes an angle with the strike of the folds. He attributes 

 the difficulties which have hitherto attended the solution 

 of the geological problems here : — 



