606 MISS M. M. OGILVIE [mES. GOKDON] ON THE [Aug. 1 899, 



seemed to rest conformably upon the Dachstein Limestone of the 

 western side, and it was difficult to think how Dachstein Limestone 

 could form the highest summit. Nearer investigation brought out 

 rather complicated relations. Dachstein Limestone in its highest 

 fossiliferous horizons forms the Boe summit. It is part of an 

 overcast fold from the south and south-east, with the C-shaped 

 curvature towards the north and north-west, while the brick-red 

 earthy strata are part of an attenuated and sheared series of 

 Jurassic rocks which lie in the trough of the overfold (fig. 18). 



Fig. 18. — Infold of Jurassic rocks ^ viewed from the east, and 

 showing the compression and shearing of the strata. 



Boe' Sumnifi. M 



DK = Dachstein Kalk. | Jar = Jurassic. 



The Jurassic infold is favourably exposed for examination. The 

 Yal la Stries or western aspect is at once the simplest and the 

 most complete. The various horizons of Jurassic rock are found to 

 be stretched, and therefore thinned, from north to south along a 

 shear-plane of Dachstein Limestone. Thus, Liassic rocks occupy 

 the terrain partially covered by the Pissadoi Glacier, while the 

 younger brick-red marls ( Pleckenmergel ) and nodular shales 

 and limestones of higher Jurassic horizons occur nearer the Boe 

 summit. Haploceras Stazyczii (Zeuschn.) was met with in the higher 

 horizons. The fossils found in the Liassic limestone-rocks were 

 numerous, but badly preserved, chiefly ammonites belonging to 

 the JEgoceras angulatum-zone. The shear-surface of the Dach- 

 stein rock is undulating, and is penetrated by several vertical 

 chasms, some of which have undoubtedly a structural import. 



A well-marked fissure separates the Dachstein-rocks of the Boe 

 summit from the contorted Jurassic marls immediately north of it. 

 The fissure denotes the reverse plane of movement with downthrow 

 on the side of the marls. Eadial dislocations penetrate the infolded 

 strata, radiating westward. These meet the reversed fault of the 

 Boe summit in a basin of Dachstein strata on the east side of the 

 ridge. The basin is occupied by a small lake, the Eis See. 



Just as in the case of intersection of a shear-plane at the Bova 

 Alp, the plane of the overthrust undergoes a sharp curvature at the 

 point of intersection, and is twisted almost due north, slightly north- 

 north-east. The reverse plane becomes then almost vertical, and 

 faults Dachstein Dolomite against Liassic and other Jurassic strata. 

 The Jurassic strata thin out from west to south, where the radiating 

 faults diverge, but are strongly crumpled and compressed on the 

 east, where the faults converge. The radiating faults through 



