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Now, for the first time, vast masses of basalt and dolerite are extruded both from vents of eruption and fissures; and, owing to their extreme viscosity, spread themselves far and wide until they reach the margin of some uprising ground of old Palæozoic or Metamorphic rocks by which the volcanic plain is almost surrounded.
The high crags which here shoulder the Wall are part of the Great Whin Sill, an intrusive dyke of dolerite which stretches from Greenhead northeastward across the county nearly to Berwick.
Professor Gustavus Rose, to whom I submitted specimens of this dike, found it to be dolerite, and composed of greenish black augite and Labrador feldspar, the latter being the most abundant ingredient. A small quantity of magnetic iron, perhaps titaniferous, is also present.
Mauna Loa and Kilauea, in the Hawaiian Group, according to Professor J. D. Dana, are basalt volcanoes in a normal state. They have distinct craters, and the material of which the mountain is formed is basalt or dolerite. The volcano of Rangitoto in Auckland, New Zealand, appears to belong to this class.
The shelve of the beach saved the cave from being flooded and the beetling of the cliff kept it dry and within a couple of feet of the entrance but it could not keep out the rain smell, the raw smell of Kerguelen carried from inland, the smell of bog patches and new washed dolerite and bitter vegetation, keen, like the smell of the Stone Age. Then after a bit the first great onslaught slackened.
The rock of which it is formed consists of exceedingly massive, coarsely-crystalline dolerite, rich in olivine, and divided into large quadrangular blocks by parallel joint planes.
The land is extraordinary gigantic snow drifts like huge waves breaking against a stone pier beset the lower cliff faces and steeper slopes, then dark red-brown rock carved by glaciers long since vanished, and above this rocky bands of limestone, sandstone; and dolerite. Some rocky talus showing through the big snow drifts, and in some cases talus alone.
The mass assumes at the surface a yellowish crust like dolerite and basalt. In the midst of this tract of trap-formation, the Morros of San Juan rise like two castles in ruins. They appear linked to the mornes of St. Sebastian, and to La Galera which bounds the Llanos like a rocky wall.
Material: a grey or a white limestone most usual; tufa and dolerite also used. Flint carved and engraved cylinder- seals, of limestone, black basalt, jasper, diorite, &c. Shell. Very largely used for decoration; small plaques of nacre often engraved with scenes of men worshipping, &c. Seal-cylinders of shell. Wood. Burials.
Here the difficulty seems to arise from the too intimate and too numerous relations observed in rocks that are thought not to belong to the same family. I found no real basalt or dolerite; but the presence of pyroxene in the amygdaloid of Parapara leaves little doubt of the igneous origin of those spheroidal masses, fissured, and full of cavities.
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