Geology : chemical, physical, and stratigraphical / by Joseph Prestwich.

  • Joseph Prestwich
Date:
1886-1888
Catalogue details

Licence: Public Domain Mark

Credit: Geology : chemical, physical, and stratigraphical / by Joseph Prestwich. Source: Wellcome Collection.

    655/710 (page 557)
    As before mentioned (Vol. I. p. io), above nine-tenths of the Earth s crust consist of those elements which, on the assumption of the external position of the metalloids, would constitute the outer layers of the nebular mass. Thus oxygen and silicon alone constitute, on the average, of the mass of the outer layer of acidic rocks ; while beneath it are the basic rocks, into the composition of which calcium, magnesium, and iron, com- bined with oxygen, enter in the proportion of, say, xrnr j while the propor- tion of the silica is less by TVV: still deeper lie the denser and harder metals, which reach the surface through fissures traversing the outer layers. The reader will not fail to remark, in the above observations, that silicon, which enters so largely into the constitution of all the rocks, does not appear amongst the substances of the Solar atmosphere. The lines of oxygen are so obscure that they have only been recently detected in the Sun; while those of silicon have as yet altogether escaped observation. Even, however, in rocks where these substances are present in large pro- portion, the spectroscope gives, as in the Sun, no signs of their presence. In a preliminary examination, kindly made for me some time ago by Lockyer, of two specimens of igneous rocks, the following were the results given by spectroscopic analysis :— Constituent Substances Lava. Greenstone, Present in the of the two rock Specimens. Clee Hill. Solar Atmosphere. Oxygen ) Silicon ) not shown not shown \ * \ not detected. Magnesium ... ? ... ... ? ... ... * Aluminium ... * ... ... * ... * Calcium Sodium ... . ) ... * ••• traces ... ... * ... ... * Potassium ... ] ... * ... ... * Manganese ... ? ... ... ? ... Iron ... * ... ... * ... ... * Meteorites. Another argument in favour of the unity of the elements throughout the Solar System is furnished by the Meteorites (see Vol. I. p. 150), which so often fall from outside space. It is only with the denser or more solid masses that we are concerned. The more nebulous masses become so heated in coming in contact with our atmosphere that they are burnt and dissipated before reaching the Earth. But the more solid and resisting masses, the Aerolites, though fused externally, and often shattered into fragments, are constantly falling on the surface of the Earth, and prove to be not only telling witnesses of the original com- munity of the elements, but also corroborate to some extent what has been inferred theoretically with respect to the order of succession of the