9. Draw diagrams showing by dotted lines the conditions both of A and B, [Figure 196], after deformation had given the strata their present attitude.
Fig. 197. A Block Mountain
10. What is the attitude of the strata of this earth block, [Figure 197]? What has taken place along the plane baf? When did the dislocation occur compared with the folding of the strata? With the erosion of the valleys on the right-hand side of the mountain? With the deposition of the sediments efg? Do you find any remnants of the original surface baf produced by the dislocation? From the left-hand side of the mountain infer what was the relief of the region before the dislocation. Give the complete history recorded in the diagram from the deposition of the strata to the present.
| Fig. 198. A Faulted Lava Flow aa´ | Fig. 199. Measurement of the Thickness of Inclined Strata |
11. Which is the older fault, in [Figure 198], f or f´? When did the lava flow occur? How long a time elapsed between the formation of the two faults as measured in the work done in the interval? How long a time since the formation of the later fault?
12. Measure by the scale the thickness bc of the coal-bearing strata outcropping from a to b in [Figure 199]. On any convenient scale draw a similar section of strata with a dip of 30° outcropping along a horizontal line normal to the strike one thousand feet in length, and measure the thickness of the strata by the scale employed. The thickness may also be calculated by trigonometry.
