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NEW YORK STATE MUSEUM 



All the facts bearing on these points seem intelligible and 

 rational. They are in accord with the teachings of physics and 

 thus are what we should naturally expect to find in this field. 



The principal structural features to which allusion has been 

 made, are commonly known as anticlines, synclines and mono- 

 clines. The first of these terms is applied to a roof-shaped 

 arrangement of the strata of a district, in which they decline in 

 opposite directions from a given line called the axis. Some- 

 times the descent on the opposite sides is equal in amount, but 

 more frequently it is unequal. The axis can generally be fol- 

 lowed for a few miles in an approximately straight line, but in 

 many cases its elevation is gradually lost. From the point where 

 it thus disappears, it is quite likely to rise again in the same 

 general direction and at perhaps the same elevation that it origi- 

 nally had. Of course, in such cases, all the fragments are 

 counted as a single axis. Wherever a well-defined axis is found, 

 one or more similar lines of structure are very likely to occur, 

 approximately parallel to the first. 



A syncline is a form of arrangement of the strata exactly 

 opposite to the anticline already described. The strata are bent 

 into a trough, instead of into a ridge. All the statements as to 

 the amount and direction of the descent of the different sides 

 that have just been made as to anticlines are to be applied to 

 synclines, with the proper, i. e. reversed, qualifications. In a 

 word, a syncline is the normal complement of an anticline, 

 and when two parallel anticlines occur, the space intervening 

 between them is necessarily occupied by a syncline. 



A monocline is in effect an incomplete anticline or syncline. 

 A stratum descending from an approximately horizontal posi- 

 tion at a certain level to a lower level regains the original hori- 

 zontal position after making the descent. It is as if nature be- 

 gan to build an anticline or syncline and was not able to finish 

 it. Monoclines are of much less frequent occurrence than anti- 

 clines and synclines. 



All these forms of structure are necessarily effected in the 

 differentiation of the contents of a porous stratum. The water, 

 which has been named as one of the three principal elements 



