CHANGE OF POSITION OF STRATA 



CHANGE OF POSITION AND DISLOCATION OF STRATA ATTRIBUTABLE 

 TO UPHEAVAL. 



10. It has been already stated that sand and shells are deposited, 

 under water, in horizontal beds. Indeed, we frequently find them 

 in this position on the surface, even over extensive spaces, and we 

 then find flattened pebbles, valves of oysters, and other shells, lying 

 flat, and turriculated shells lying on one side ; and everything con- 

 firming the idea of a slow formation, by the weight of these sub- 

 stances. But it sometimes happens that we see deposits, more or 

 less inclined in certain parts of their extent, raised up almost to a 

 vertical position, and sometimes entirely overturned ; they still 

 preserve, however, all the characters which show they were at first 

 horizontal, for the debris of shells and pebbles they contain are still 

 found arranged parallelly to the planes of the beds. Besides, there 



are deposits which contain ge'odes 

 of agate, in which are found sta- 

 la'ctites with the axis more or less 

 _ inclined (Jig. 253), which is di- 

 rectly opposite to the manner of 

 production of these substances. 

 Consequently, these deposits could 

 Fig. 253. Fig. 254. no t have been formed in the posi- 



tion we find them, for, on the one hand, the debris of shells and 

 pebbles would have rolled over to be surely balanced, or fallen to 

 the foot of the talus ; on the other, the stalac'tites would have formed 

 in a vertical position. This last observation, particularly, shows 

 that the beds were at first horizontal (Jig. 254), and that their posi- 

 tion has been changed subsequently to their formation; this is one 

 of the great geological phenomena we seek to explain. 



The effects of earthquakes, and those of volcanic phenomena, will serve as 

 points of comparison in our inquiry. On one hand, the crevices produced 

 in the soil at the time, to a greater or less depth, can only be the effect of 

 upheaval ; for the separation of parts does not result here from drying, nor 

 from cooling, which would produce a retreating of the whole mass. It is 

 remarked, in the neighbourhood of cracks, that the soil is no longer on the 

 same plane as the rest of the country; that it is more or less arched, and 

 often one part is more elevated than another. Now, if the soil have been 

 uplifted, it must follow that the internal beds have been disturbed in their 

 position ; consequently, when in a formation of horizontal strata, a crack is 

 made in a straight line (fig. 255), the beds must be inclined on both sides 

 through their length, like the two slopes of a roof. When several divergent 

 cracks are formed (fig. 256), the beds ought to incline symmetrically around 

 the axis of elevation. 



Now, if we find all inclined beds in one or the other of these positions, 

 we have a right to conclude they have been uplifted by the same causes. 

 ll. Faults. When a crack is made, it often happens that one 



10. What proves that the position of strata has been changed by up 

 neaval ? 



