Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . p contains clear evidence to thecontrary. Example* The width of an outcrop is 1 mile at a place whereit is crossed by the line of a proposed excavation. There INCLINED AND FOLDED STRATA 55 is no dip arrow near this place, but at a point where adip of 20° is indicated, the outcrop is only half a milewide. Then taking 6 as the angle of dip required, andassuming the thickness of strata to remain unchangedand the surface of the ground to be horizontal, sin t ;= n,U sin 0 2 2 sin^0° 2?
Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . p contains clear evidence to thecontrary. Example* The width of an outcrop is 1 mile at a place whereit is crossed by the line of a proposed excavation. There INCLINED AND FOLDED STRATA 55 is no dip arrow near this place, but at a point where adip of 20° is indicated, the outcrop is only half a milewide. Then taking 6 as the angle of dip required, andassuming the thickness of strata to remain unchangedand the surface of the ground to be horizontal, sin t ;= n,U sin 0 2 2 sin^0° 2? -342sin 6= -34:2/2 = 171. On consulting a table of natural sines, it will be found that•171 is the sine of 9° 51, which is therefore the angle ofdip required. Apart from the actual calculation of the angle of dip,it may generally be assumed that where the outcrop of a —» miliumItiiiniit IlllUIII Allium inn—* o o o o - 0 o o o 40 ////^/// 10 iilli201 miilliuiigliiliini |||H|IIM °30 ? o .o o ? - „iii|iiin 0 0 ///////// [[NUUiil iiitiiimi 0 0 o o .. ?\-f///////, itlMllnil O Q (a) rock is narrow the dip is steeper than where the bed occu-pies a wider belt of country. In this connection it must be borne in mind thatinclined beds are in most instances parts of folds (see p. 31),and that, as a consequence, the dip of a bed varies con-tinuously, and it must be remembered that the dip arrowand the figures attached to it merely indicate the dip atthe point of the arrow and at the surface of the ground. In drawing sections, therefore, care must be taken topreserve the thickness of the various strata unchanged,except where changes of thickness are clearly in the example, Fig. 29 (a) it will be seen that thearrows on each bed of rock indicate a different amount ofdip, but the beds must not be supposed to thin out as 56 GEOLOGICAL AND TOPOGRAPHICAL MAPS indicated in the section (b), but to curve round graduallyas in (c). On steep slopes the outcrops o
Size: 1721px × 1451px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeology, booksubjectt
