244 The Physical History of the Trias 



which every fact, as it came to our notice, seemed to have had 

 a place pre-arranged for it in the course of events which we 

 are seeking to follow. We lind this to be the case, also, with 

 the Triassic traps. From their uniformity of structure and 

 composition in both New Jersey and the Connecticut Valley, 

 and from the striking analogy in their geological arrangement 

 in the two areas, the decision seems inevitable that all these 

 various sheets and dikes of trap must have a common history. 

 This conclusion is especially indicated by the fact that the trap 

 rocks are almost entirely confined within the borders of the 

 red sandstone regions; and not only is this the case in the 

 localities mentioned above, but also in every Triassic area along 

 the Atlantic coast. 



If we now return to our view of the previous condition of 

 the Triassic sedimentary beds, viz., that they were spread out 

 as horizontal layers of sediment at the bottom of an ancient 

 estuary, we shall be able, I think, to find the place in the his- 

 tory to which the trap rocks should be referred. We have 

 shown that the bottom of this ancient estuary must have been 

 upheaved, in order to place the stratified rocks along its borders 

 in the position which they now occupy. It may be that this 

 upheaval was due to the formation of another anticlinal fold 

 like those of older date which form the Appalachian mountains 

 to the westward. But it also seems as if, in addition to this 

 folding of the strata, there must have been a force acting ver- 

 tically upward. This movement was the reverse of the slow 

 subsidence which had previously taken place, and which allowed 

 the shallow- water deposit to attain such an immense thickness. 



It is evident that when such a great movement of the earth's 

 crust occurs, a time will come when the flexure of the rocks 

 is no longer possible, and fracture must take place. The ques- 

 then arises as to where such fracturing will occur and what 

 will be the direction of the fissures formed. We have, as the 

 first condition of the problem, an immense basin-shaped depres- 

 sion in the crystalline rocks, — a hundred miles in its shorter 

 diameter ; the elevation of an area fifty to seventy miles wide 

 takes place along its longer axis. The line of greatest strain wil 



