340 THE VOYAGE OF THE 'DISCOVERY [Appx. 



bottom, are about twelve feet in diameter. The Nunatak is about 

 sixty miles from the coast, at an elevation of about 8,000 feet, and 

 appears to be part of the great sheet capping the sandstone five or 

 six miles to the eastward. 



This sheet, on the east side or the South-West Arm, is quite 

 similar in outward form to Depot Nunatak, and rises some 

 700 feet in an almost sheer cliff. Locally portions of sandstone 

 have been lifted bodily by the dolerite, and the junction specimens 

 prove that the dolerite is the younger rock. A great pipe fifty 

 yards in diameter bursts vertically across the bedding planes of the 

 stratified rock, and appears to feed the sheet, which extends con- 

 tinuously as far as Finger Mountain. 



At the Inland Forts on the north side of the Ferrar Glacier 

 the hills rise to a very uniform height and are capped by dolerite. 

 Two or three small pipes rise through the sandstone, but these 

 could hardly have supplied an appreciable proportion of the great 

 mass above. 



Finger Mountain rises 500 feet above the ice, and is composed 

 of alternate layers of sandstone and dolerite. Near the ice- 

 cascade the lowest rock visible is part of the Beacon Sandstone 

 formation, and above this is a sheet of columnar dolerite which 

 unites with another sheet on the west side of the hill. These 

 two sheets are partially separated by a wedge of sandstone half a 

 mile long, and the wedge is 200 feet thick, where it is cut off by 

 the eastern slope of the hill. The bedding planes are horizontal, 

 and are made conspicuous by the metamorphic action of the 

 dolerite. Where the dolerite sheets are in contact the columns 

 are continuous and vertical, but where the sandstone intervenes 

 the columns of the upper portion have a slight tilt to the west. 

 Here also numerous dykes and sills prove the intrusive nature of 

 the dolerite. 



These same relations were observed in the Dry Valleys and on 

 the Terra Cotta Hills, and need not be reiterated. 



The summits of both the Beacon Heights, of New Mountain 

 and of Knob Head appear to consist of dolerite ; and in all 

 four a second sheet, almost identical with the lower sheet in 

 Finger Mountain, separates 200 feet or so of sandstone from 

 the main mass which forms the greater bulk of the said 

 mountains. 



At the foot of New Mountain and at the foot of Knob Head 

 there is another sheet of dolerite. The outcrop at the last spot. 



