Page:The South Staffordshire Coalfield - Joseph Beete Jukes - 1859.djvu/230

212 yard or foot in so many yards or feet. The following table gives the latter number for each of the angles mentioned.

Another table that is often found useful in geological surveying is one that for every degree of dip of a bed, Ac. will give its depth from the surface (supposed to be a horizontal plane) at a distance of 100 feet or yards, measured in the exact direction of the dip. In the following table this is given for every degree up to 20°, and for every five degrees after that; and also the thickness of any set of beds thus inclined, measured, not perpendicularly to the surface but perpendicularly to the dip, in other words, the thickness they would have if they were horizontal.

As this table is one giving the solution of a right-angled triangle for each angle specified, it may be readily used to find any dimension which can be stated in the form of a right-angled triangle, as for calculating the space between the outcrop of two beds, of which the angle of dip is known and the thickness between them; the distance which any bed, of which the depth and inclination are known, will require before its outcrop at the surface can occur; and so on.

By means of this table, also, the probable "throw" of faults can be ascertained, where the broken ends of a bed on opposite sides of a fault