Archive image from page 280 of Discovery Discovery discovery0304londuoft Year: DISCOVERY 271 hundred yards, then the gradient rapidly rose up the face of a mountain. Deep ravines laid bare a succes- sion of sedimentary strata i,ooo feet or more in thick- ness, over which had been piled layer after layer of lava-flows and beds of volcanic ash. The widely spread sheets of basalt (in some places as many as thirty superposed la-ers), which give a terraced appearance to the weathered face of the cliffs like that of the rocks of Mull and other islands off the west coast of Scotland, are proof of
Archive image from page 280 of Discovery Discovery discovery0304londuoft Year: DISCOVERY 271 hundred yards, then the gradient rapidly rose up the face of a mountain. Deep ravines laid bare a succes- sion of sedimentary strata i,ooo feet or more in thick- ness, over which had been piled layer after layer of lava-flows and beds of volcanic ash. The widely spread sheets of basalt (in some places as many as thirty superposed la-ers), which give a terraced appearance to the weathered face of the cliffs like that of the rocks of Mull and other islands off the west coast of Scotland, are proof of long-continued volcanic activity on a stupendous scale. The photograph (Fig. 2). taken near the Arctic Station on Disko Island after a recent fall of snow, shows very clearly the layers of lava and ash above the talus slopes. The darker rocks in the foreground belong to the much more ancient crystalline series which forms the greater part of Greenland. Another expression of volcanic phenomena is seen in the numerous dykes which frequently cut across the beds of sandstone and shale. A dyke con- sists of some igneous rock, often basalt, that has been forced from below through cracks and fissures in the overlying strata. The softer rocks fall an easier prev to the action of the weather than the harder and more compact dj-kes, which are left as great ribs or dark-brown buttresses projecting on a light-yellow background of less resistant material. Part of a dyke of dark-brown basalt is seen at close quarters in Fig. i; it resembles a partially ruined wall on a wind-worn denuded field of sand, the result of disintegration of beds of soft sandstone. Here and there adhering to the sides of the dyke are blocks of sandstone which were hardened and rendered more resistant to denuding agents by contact with the molten rock which welled up against their fissured sides. From the beds of shale exposed in the cliffs on the south coast of Upernivik Island (lat. 71 N.) above the beach, littered
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