The use of this table is obvious without much explanation. A single example will suffice. Suppose a section be drawn running north-east and south-west, and it crosses certain beds dipping north at 35° (or certain cleavage planes, or a vein, or a fault, or any other plane having that dip), what angle ought we give to those beds in the section in order to give a true representation of the apparent dip they would have in a cliff running parallel to the section?
In this case the angle between the direction of the dip and that of the section, or between north and north-east = 45°; which we look for in the vertical column on the left of the table, the angle of the dip = 35°, which we find in the horizontal column at the top of the table. At the intersection of these two lines in the body of the table we should find 26° 15', the angle required.
In practice the minutes of the angle are never required, but as it involved no extra trouble to insert them they are given, as the table might possibly be of use in other ways where more minute accuracy is requisite.
It is plain that the table can be equally used to find the true dip where the apparent dip only can be observed in a real cliff, provided the angle between the line of section and the strike (and therefore the direction of the true dip) of the beds can be ascertained. This, however is a case which rarely occurs in practice. When it does, of course the nearest angle to the observed apparent dip will be sought in the body of the table, on the line opposite to the angle between the direction of the cliff and that of the strike ± 90°, and the angle of the real dip answering to it will be found at the top of the table.
Note on the Stigmaria Beds of the South Staffordshire Coalfield. By Sir Henry de la Beche, C.B.. F.R.S., &c.
The coal-field of South Staffordshire forms no exception to the other coal-fields of Great Britain as regards the occurrence, in certain of its beds, of the peculiar fossil roots known as Stigmaria, in their relative places of growth. These vegetable remains, long considered as the stems of a distinct fossil plant, are now known, chiefly through the researches of Mr. Binney[1] in England, and of Mr. Brown[2][3] in Nova Scotia, to be the roots of the fossil genus Sigillaria, or of some other of the like kind of plants.
Mr. Steinhauer would appear (in 1818) to have been the first to have observed the mode of occurrence of Stigmaria in certain beds of the coal measures, in a manner pointing to their growth in the bed where they are thus found. Speaking of the rootlets or fibres, as he terms them, diverging from the main Stigmaria root, he remarks that "on examining
- ↑ Mr. Binney's observations respecting the trees discovered at St. Helen's. Lancashire, were made known to the meeting of the British Association for the Advancement of Science, in June 1845, and his description of the Sigillaria terminating in Stigmaria, found at Duckinfield, seven miles east of Manchester, was read before the Geological Society of London, in April 1846, and published in their Quarterly Journal, with figures, vol. ii, p. 390.
- ↑ Mr. Brown read a paper before the Geological Society, on the same day (22nd April 1852), with Mr. Binney's last-mentioned paper. It is also published in that Society's Journal, vol, ii., and is entitled "On a Group of Erect Fossil Trees, in the Sydney Coal-field at Cape Breton." He gives figures of an upright Sigillaria stem with branching Stigmaria roots.
- ↑ Brown, Richard On a Group of Erect Fossil Trees in the Sydney Coal-Field of Cape Breton. Quarterly Journal of the Geological Society, 2, 393-396, 1 February 1846, doi:10.1144/GSL.JGS.1846.002.01-02.54 (Wikisource contributor note)
