Geology of Northwestern Spitsbergen. 423 



exact advance of a big glacier at Cross Bay, the Liliehook 

 Glacier, has been noted. A large stone placed on the surface 

 of the glacier 200-300 ra. from the margin advanced : 1908-9, 

 338 m.; 1909-10, 200 m. ; 1910-11, 183 m. ; 1911-12, 77 m. 



The chief tectonic features can be seen from the geological 

 maps and the sections. The general direction of the fault lines 

 is NNW-SSE, parallel to the strike of the Heclahook rocks. 



Regarding the age of the dislocations, the Red Bay fault is 

 probably very old, as the red Wood Bay beds, farther south, 

 do not seem to be affected by it. The down faulting of the 

 Tertiary areas, and probably the big fault along the west coast, 

 are of post-Miocene age. There was observed, however, in 

 Prince Charles Foreland, a feature that seems to indicate that 

 this great dislocation has continued since an older time. The 

 Tertiary beds are there seen to rest directly upon the Hecla- 

 hook, ail the younger formations having been eroded away in 

 pre-Miocene time. This erosion is therefore most naturally 

 explained by an early uplift of this western region. 



An interesting feature in connection with the big fault that 

 separates the Heclahook horst on the east of the Foreland 

 Sound from the great eastern down-sunken area, is the tectonic 

 disturbances near the fault line, telling of an immense tangen- 

 tial pressure. The finest illustration of this is seen on Brog- 

 ger's Peninsula, where a great sheet of Heclahook schists is 

 pushed several kilometers to the north over the Carboniferous 

 limestones. 



The age of the fault on the west side of the Wood Bay 

 Series, running nearly in a straight line for 80-90 km , cannot 

 as yet be fixed with certainty. There are several facts that 

 seem to indicate an early pre-Carboniferous age, which would 

 mean that we have here one part of the western limit of that 

 Graben of which the pre-Carboniferous Wijde Bay fault is the 

 eastern. 



That the fault line has very recently been also a line of weak- 

 ness is shown by the occurrence of young volcanic masses that 

 in two places are situated directly upon it.* At one place, in 

 Bock Bay, can still be seen the well-preserved remnants of a 

 volcanic cone, 500 m. high, built up of lapilli and tuffs, often 

 with bombs, and crossed by lava veins. The rock in these is 

 trachydolerites, rich in alkalies, and thus different from the 

 ordinary young volcanic rocks of the northeastern Atlantic 

 region. The Bock Bay volcano is certainly of Quaternary age, 

 as it is situated near the bottom of an ice-eroded valley, and 

 the lava streams commonly contain boulders, originally belong- 



* See Hoel and Holtedahl : Les nappes de lave, les volcans et les sources 

 therniales dans les environs de la Baie Wood au Spitsberg, Videnskapsselsk. 

 Skrifter, I. Mat.-Naturv. Klasse, 1911. 



