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. [Illustration: 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. [Illustration: Fig. 198. A Faulted Lava Flow _aa´_] 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? [Illustration: Fig. 199. Measurement of the Thickness of Inclined Strata] 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. [Illustration: Fig. 200. Unconformity between Parallel Strata] [Illustration: Fig. 201. Unconformity between Non-parallel Strata] Unconformity Strata deposited one upon, another in an unbroken succession are said to be _conformable_. But the continuous deposition of strata is often interrupted by movements of the earth's crust, Old sea floors are lifted to form land and are again depressed beneath the sea to receive a cover of sediments only after an interval during which they were carved by subaërial erosion. An erosion surface which thus parts older from younger strata is known as an _unconformity_, and the strata above it are said to be _unconformable_ with the rocks below, or to rest unconformably upon them. An unconformity thus records movements of the crust and a consequent break in the deposition of the strata. It denotes a period of land erosion of greater or less length, which may sometimes be roughly measured by the stage in the erosion cycle which the land surface had attained before its burial. Unconformable strata may be _parallel_, as in Figure 200, where the record includes the deposition of strata _a_, their emergence, the erosion of the land surface _ss_, a submergence and the deposit of the strata _b_, and lastly, emergence and the erosion of the present surface _s´s´_.