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IV.—On the Limburgite from near Sasbach
Published online by Cambridge University Press: 01 May 2009
Extract
So much confusion has existed on the subject of limburgite, that, although it has now been partly dissipated, a record of my own investigations may be of use, at any rate to English petrologists. The rock has been classed by some with the peridotites. From these it is separated by Rosenbusch, who in his latest work places it in a subgroup with the augitites in proximity to the basalts. Zirkel uses limburgite as a synonym for magma-basalt. F. Graeff implies relationship with the nepheline-basalts. Harker's remarks suggest similar conclusions, as do those of Cole, though his opening words are perhaps slightly misleading. All, however, lay so much stress upon the absence of felspar, by giving such definitions as “Limburgite und Augitite sind die felspathfreien Entglieder der Gesteinreihe Trachydolerit, Tephrit,” etc., or “Frei von Feldspar und Felspathoiden ist der Limburgit,” and in some cases by reference to the peridotites, that students may readily overlook the fact that this rock is only free from felspar in the same sense as tachylite or many pitchstones and obsidians.
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References
page 411 note 1 “Elemente der Gesteinelehre,” p. 361. See also “Mikroscop. Physiogr. der massigen Gesteine,” p. 811.
page 411 note 2 “Mitt. der Grossher. Badischen Geol. Landesanstalt,” ii, p. 405.
page 411 note 3 “Petrology for Students,” 1895, p. 179.Google Scholar
page 411 note 4 “Aids to Geology,” 1898, p. 262.Google Scholar
page 411 note 5 Rosenbusch: “Elemente,” p. 361.
page 411 note 6 Graeff: loc. cit.
page 411 note 7 “Elemente,” p. 363.
page 411 note 8 From a pamphlet by Professor Steinmann.
page 411 note 9 Traces also of Cu and Ni.
page 412 note 1 Generally under 5·5.
page 412 note 2 Wadsworth: “Lithological Studies,” p. xxiv.
page 412 note 3 These remarks do not apply to the list given by Professor Rosenbusch, ut supra, p. 165, but from personal knowledge I must refuse to admit either the Schriesheim picrite or kimberlite into the peridotites.
page 412 note 4 As in the mica-peridotite of Kentucky.
page 412 note 5 As in the Rauenthal serpentines. Here the alumina only amounts to 1·35: see Raisin, C. A., Q.J.G.S., 1897, pp. 251, 257.Google Scholar
page 412 note 6 Pres. Add. Geol. Soc.: Q.J.G.S., 1885, p. 69.Google Scholar
page 412 note 7 This is virtually admitted by Rosenbusch (“Elemente,” p. 361, and “Mikro. Phys.,” p. 813). Zirkel (iii, 76) will not allow even this, and uses limburgite as a synonym for magma-basalt.
page 412 note 8 Professor Steinmann writes ‘Limberg’ for the place.
page 412 note 9 It is not my custom to be satisfied with specimens thus collected. But I had been unable to get a carriage at Riegel (as I had been led to expect), and thus had been obliged to go on foot. It was a hot afternoon, a long and fatiguing walk, and my time was limited by trains, so that I had to turn back without reaching the hill.
page 413 note 1 I have a couple of slices of limburgite, bought nearly as long ago. They show the usual minerals, imbedded in a rich brown glass, in which also are scattered a few microliths, apparently a pyroxene.
page 414 note 1 Neues Jahrbuch, 1872, p. 33.Google Scholar
page 414 note 2 I defer the description of these.
page 414 note 3 “Petr. Stud. an den Gesteinen Böhmens,” pl. ii, fig. 8, and pl. iii, fig. 3.
page 415 note 1 It affects only the exterior, or penetrates into some of the cracks.
page 416 note 1 Miss Raisin informs me that the specific gravity of a compact specimen is 3·058.
page 416 note 2 Herr F. Graeff (loc. cit.) also gives a section, naming the top and bottom flows in each limburgite and the middle one nepheline-basalt. He notices the different colour of the mass at the bottom of the southern quarry, and says this has a different habit from typical limburgite.