Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . n the maps of the Geological Survey the rocksgrouped in the table under the heading Ordovician arecalled Lower Silurian, while the term Upper Silurian isemployed to designate the beds Nos. 10, 11, and 12, whichabove are called Silurian. Stratification and Folding1.—It has been stated onp. 27 that sedimentary rocks are, in most instances, laid THE STRUCTURE OF THE EARTHS CRUST 31 down in approximately horizontal layers, but it is withinthe experience of those who have examined rock
Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . n the maps of the Geological Survey the rocksgrouped in the table under the heading Ordovician arecalled Lower Silurian, while the term Upper Silurian isemployed to designate the beds Nos. 10, 11, and 12, whichabove are called Silurian. Stratification and Folding1.—It has been stated onp. 27 that sedimentary rocks are, in most instances, laid THE STRUCTURE OF THE EARTHS CRUST 31 down in approximately horizontal layers, but it is withinthe experience of those who have examined rocks in thefield, that horizontal stratification is, at all events inBritain, the exception rather than the rule. The beds ofrock are frequently tilted or inclined, and in many casesthe angle of inclination varies rapidly, so that verydifferent inclinations, or dips as they are called, mayoccur in the same bed of rock within the limits of thesame quarry or cutting. The dips are due to disturbanceof the strata, subsequent to their deposition, and, in someinstances, this disturbance has been so great as to throw. Syncline Anticline Fig. 9.—Inclined Beds formed by parts of Folds. the beds into a vertical position, or, in extreme cases, togive rise to actual inversion. The diagram (Fig. 9) is intended to illustrate the rela-tionship of the various degrees of dip to each other, and itwill be seen that the inclination of the strata is not due tosimple tilting, but to folding; the names of the principaltypes of fold are indicated in the diagram. Cases alsooccur in which dip is due to a simple tilting of a block ofthe earths crust, but these are, for the most part, to beexplained by fractures of the strata, or faults, which willbe discussed later. In addition to the simple anticlinal and synclinal foldsseen in Fig. 9, other and more complicated arrangementsof the strata occur in places where one system of folds iscrossed by another, the simplest of these being the dome,or qua-qua-vers
Size: 2741px × 912px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeology, booksubjectt
