NERBUDDA DISTRICT. 



223 



sions from observations. Moreover, it is evident, that this method can be 



used only where the sedimentary rocks appear, that is at the edge of the 



trap area— a position which is a -priori improbable to have been that of 



any of the ancient centres of eruption. 



No geologist can pass through any part of this trap-area without 



being struck by the persistence of the layers of 

 Continuous beds or a J 



flows. basalt, in thickness and horizontality, over great 



distances. 



" The question of the manner of the formation of the horizontal beds 

 " of trap is very interesting. It will be said they were ejected under the 

 " pressure of an incumbent ocean. If such had been the case, where 

 f e are the marine remains ? and would there not have been sediment- 

 " ary deposits upon them ? Moreover, if viewed as coulees from craters, 

 " would not the beds have thinned out, instead of preserving the pa- 

 " rallelism of their superior and inferior planes ?" (Col. Sykes as quoted 

 above.) 



The difficulties stated by Col. Sykes in this passage must in great part 



remain for the present unsolved. Those inter- 

 Unaccounted for. ill- 



trappean beds discovered since it was written 



clearly show that the basaltic flows were not sub-marine; but I am not 



aware that any satisfactory explanation of the extraordinary parallelism 



of the upper and lower surfaces of the trap flows has been suggested 



or any cause assigned why those flows are found so uniform in their 



thickness at points far removed from each other. 



Dykes. — Among the numerous trap dykes found throughout this 



district many of the well known phenomena of the action, and habits of 



intrusive rocks may be well studied. In most of the great dykes the 



well known fact of a system of joints at right 

 Jointing at dyke wall. , 



angles to their sides, may be seen; it amounts 



often to columnar structure, the columns lying flat when the dyke is 



vertical, and being inclined to the horizon in a direction at right angles 



