^Ol* 55*] TORSION-STPvUCTTJEE OP THE DOLOMITES. 561 



dolomitic horizon (the Mendola Dolomite), followed in Southern 

 Tyrol by the Buchenstein banded limestones and conglomerates, 

 with frequent occurrence of lavas and volcanic tuffs (especially the 

 greenish pietra verde). 



(C) The succeeding horizons — named by Eichthofen Wengen strata^ 



Cassian strata, and Schlern Dolomite — are more particularly 

 those around which, together with the next horizon in the succession — 

 the Eaibl strata — the stratigraphical difficulties in the Dolomites 

 have grouped themselves. 



(D) The highest horizon of the Trias — namely, the Dachstein Lime- 

 stone which follows — has long been quite definitely determined in 

 the Dolomites. 



With regard to the group of strata (C) below the Dachstein 

 horizon, it will be remembered that when I first wrote upon the 

 subject of the Dolomites, the questions at issue were mainly con- 

 cerning the distribution of the different rock-facies in the 

 region, namely : — 



(1) Whether the massive Schlern Dolomite was the time-equivalent of 



the tufaceous shales and marls and thin-bedded limestones comprised 

 as the Wengen and Cassian Series, etc. 



(2) Whether the dolomitic rock-facies had been originally developed in 



thicknesses of 2000 or 3000 feet, forming precipitous mountain-walls, 

 and then as suddenly dwindled down to nothing amid the surround- 

 ing deposits of earthy facies. 



(3) And whether, if such were the case, the ' coral-reef ' theory ascribing 



these enormous thicknesses of rock to coralline agency accounted for 

 all the peculiarities of the district. 



The coral-reef theory was merely suggested ^ by Baron F. von 

 Richthofen in 1860 as a possible explanation of the curious 

 stratigraphical features then not easily paralleled ; but it entirely 

 permeates the brilliant work of Mojsisovics,^ and meets there with 

 an elaboration of detail which would appear to carry conviction 

 with it. 



Certain peculiarities, however, remained unexplained to the minds^ 

 of many, and Baron F. von Eichthofen pointed out to me how and 

 where some of the main problems might best be re-investigated, 

 advising, above all, a minute search for fossils in the earthy strata 

 of Enneberg, etc., and a detailed mapping of the fossiliferous- 

 zones round the base of a massive. This is the method which I 

 have followed at every available opportunity since 1891. 



In my papers, published in 1893 & 1894, I^ established the 

 following conclusions respecting the question of local lithological 

 facies : — 



(1) The Schlern Dolomite was originally a single sedimentary sheet 

 overlying the earthy, thinly-bedded Wengen and Cassian strata 

 throughout Grroden, Enneberg, and Ampezzo. 



^ An account of the first enunciation of this theory by Eichthofen, th 

 opposition which it received at the hands of the late C. W. von Giimbel and 

 Prof. Lepsius. and the strong support from E. von Mojsisovics, has been pre- 

 viously given bv the present author, op. cit., Quart. Journ. Geol. Soc. vol. xhx 

 (1893) pp. 4-12. 



2 ' Die Dolomit-Eiffe von Siid-Tirol u. Venetien,' Vienna, 1879. 



3 Op. cit. Quart. Journ. Geol. Soc. vol. xlix, p. 47; and 'Coral in th 

 Dolomites,' Geol. Mag. 1894, pp. 1, 49. 



Q. J. G. S. No. 219. 2 



