382 MR. A. V. JENNINGS ON THE [Aug. 1 899, 



its breccias, are all questions which no student of the Alps can 

 ignore, and in the study of which he may here expect to find help. 



The following account does not pretend to be complete or 

 exhaustive. It is a summary of the results of observations made 

 during 1898, with the addition of notes jotted down in several 

 previous years. 



Prof. Theobald's map and the accompanying memoir, published 

 in 1864, are splendid examples of the results obtainable by the 

 ■enthusiasm and energy of a single student ; but they necessarily 

 require revision with the advance of knowledge, and are also 

 beyond the reach of many who might obtain and read a shorter and 

 more concise account. Prof. Steinmann has studied the district 

 on the west round Arosa, and Prof. Tarnuzzer has worked at the 

 structure of the Rhatikon. Dr. John Ball has investigated certain 

 of the Davos rocks, but his work was petrographic rather than 

 geological. There has been, I believe, no general account of the 

 geology of the district, though many of its problems have been dealt 

 with by Heim, Rothpletz, Mojsisovics, Diener, and others. 



The following works are those to which references will be found 

 in the ensuing pages : — 



Theobald, 1864. — Beitr. Geol. Karte d. Schweiz, 2te Lief. Sheet 15 & accom- 



panyiBg memoir. 

 Taenuzzee, 1891. — ' Der geologische Bau des Rhatikongebirges.' Jahi-esber. d. 



Naturf. Gesellsch. Graubxindens, vol. xxxv. Chur. 

 Steinmann, 1897. — ' Das Alter der Biindner Schiefer,' Ber. Naturforsch. Gesellsch. 



zu Freib. i. B. vol. ix, pp. 245-263 & vol. x, pp. 215-292. 

 Ball, 1897. — ' The Serpentine & Associated Rocks of Davos.' Dissertation for 



degree of Doctor of Philosophy. Ziirich. 

 Bodmeb-Bedee, 1898. — 'Ueber Oliviudiabase aus dem Plessurgebirge.' Neues 



Jahrb. Beilage-Band xii, p. 238. 

 Heim, A., 1878. — ' Untersuchungen iiber den Mechanismus der Gebirgsbildung, 



Basel.' 

 Paeona, 1891-92. — ' Sugli Schisti silicei a Radiolarie di Cesana presso il Mon- 



ginevra.' Atti R. Accad. Sci. Torino, vol. xxvii, pp. 305-319. 

 Paeona & Roveeeto, 1895. — 'Diaspri Permiani a Radiolarie di Montenotte 



(Liguria occidentale).' Atti R. Accad. Sci. Torino, vol. xxxi, pp. 167-181. 



Position and General Geological Structure of the 

 District. 



The Davos Yalley runs approximately north-east and south-west, 

 roughly parallel to the Yorder Rhein. Its present southern out- 

 flow is by the Landwasser, which joins the Albula at Filisur. On 

 the north a smaller stream flows into the Landquart at Klosters, 

 and thus the drainage from either end is ultimately into the Ehine. 



The quadrilateral area between the Albula and Landquart, 

 Landwasser and Vorder Phein, is deeply incised from east to west 

 by the Plessur, flowing into the Ehine at Chur. The watershed of 

 the latter is the ridge of mountains west of Davos, forming the 

 Aroser-Pothhorn group on the south, and stretching northward 

 towards Klosters. Thus, on the west of Davos there is a mountain- 

 ridge crossed only by foot-passes, the Parsenn-Furka Pass, the 

 Strela Pass, and the Mayenfelder-Purka Pass. On the east are the 



