. Introduction The eastern part of Iceland is built mainly of a great series of plateau basalts dipping at low angles to the west, and the structure is magnificently exhibited in the sides of the deep valleys and fjords which incise the 3000–4000-foot plateau. The traveller is impressed by the constancy of the almost flat-lying trap featuring, which persists in the region of the ‘stock’ intrusions to the south (Cargill et alii , 1928), so that Sandfell, a hill of light-coloured rock on the south side of Faskrudsfjord, at once attracts attention because the basalts are disposed at high angles in proximity to it—a circumstance which was noted by Thoroddsen (1906, pp. 268, 277). The hill is a splendid example of a laccolith similar in type to those of the Henry Mountains, Utah, and equally impressive in its exposure. The combination of conditions which made the intrusions of the Henry Mountains the type of their class is present here—approximately level strata, intense erosion, and absence of vegetation (Gilbert, 1877, p. 97). The main hindrance to the complete elucidation of the structure is the extensive screes—to which Sandfell owes its name. This paper is based upon field investigations made on four visits between 1914 and 1932. In the earlier stages of the work snow-drifts hid some of the higher parts, but there has been a marked amelioration of climate in latter years, and in August 1932 all the drifts had disappeared. The district is unmapped, and in 1928 the second author made
Summary The 163 erratics from the Cambridge Greenland in the Sedgwick Museum, Cambridge, comprise about 40 types of sedimentary, igneous, and metamorphic rocks. Two boulders may be matched with the paisanite of Mynydd Mawr, North Wales, others with the Uriconian rocks of the Midlands and Welsh Borders, whilst the majority, two of which are of types unknown in the British Isles, cannot be localized. The boulders were floated to the Cambridge region, probably in the roots of trees, during the long period of the formation of the Greensand deposit. They prove the existence of land in North Wales and other areas in Cambridge Greensand times. I. Introduction The Cambridge Greensand, a glauconitic marl 1-2 and one-half feet thick, rests on the Gault, and in places with obvious disconformity (Jukes-Brown 1875 ; Reed 1897, p. 96). Between 1854 and 1909 it was worked for phosphate nodules at many localities from Sharpenhoe (Bedfordshire) to Soham (Cambridgeshire) (Strahan 1916), a distance of over 50 miles. Sedgwick writes in 1858 : “Many hundred men are employed in turning out this (so-called) coprolite bed, and many steam engines are working to wash out the phosphate nodules” (Clark and Hughes 1890). “Immense tracts of land in the neighbourhood of Cambridge were turned over” (Jenyns 1867), the nodule bed being only a few feet from the surface, and Sedgwick (1846) states : “The Greensand though partly incoherent and of such inconsiderable thickness, yet appears to have protected the upper surface of the gait from denudation,
The intrusions of plutonic habit in Iceland have their greatest development in the south-east of the country, and our present knowledge of them is summarized by Thoroddsen, who gives the location of the main occurrences (VII, pp. 264–87). Beyond this little is known of the relationship of the intrusions to the country- rocks or their petrological character; there is one short paper by Helland dating from 1884 (V). The present study is the result of four summer field excursions by the second-named author, and one excursion by his collaborators, who are responsible for the section on the Slaufrudal stock only. Some intrusions have been mapped on the ‘Generalstabens Topografiske Kort’ (1: 50,000) ; but this map is not yet completed, and more detailed work on certain areas is on that account held up. The country-rocks are mainly plateau-basalts of Tertiary age, with some rhyolitic lavas, tuffs, and breccias, having a north-westward to west-north-westward dip of 5° to 20°, and cut by numerous dyke-intrusions of a regional north-easterly to north-north-easterly trend. Some of the gabbros are beneath the Vatna Jökull ice-cap, and are represented by pebbles in the southern outwash fans. The outcrops of the rocks here described are indicated on the sketch-map (fig. 1, p. 506).
Northern Iceland between Skagafjord on the west and Skjalfandi Bay on the east is a deeply dissected upland built up of plateau basalts with subordinate intercalations of clastic volcanic sediments. The main valley, the Eyjafjord, is traceable northwards as a groove in the sea floor down to–500 metres. To the east of the upland the country is less elevated; marine Pliocene deposits are present in the Tjörnes peninsula, and recent lava flows are prominent. The contrasted regions adjoin along the BarQardal fault running N.–S. and marking the western boundary of the great graben which has been the site of Recent and Quaternary volcanic activity. Thoroddsen considered the upland rocks to be Tertiary (Miocene) in age, and that the Pliocene sediments had been laid down in a bay formed after the faulting and erosion of the older series.
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