146 



GEOLOGY. 



Fig. 75. 



Fig. 76. 



in which the fissure was made, then the denudation 



which followed left what 

 is called a sunk dike, as 

 seen in Fig. 75. But if, 

 as is usually the case, the 

 fissured rocks were soft- 

 er than the trap, it left a 

 raised dike, as represented in Fig. 76. Hugh Miller, in 



commenting upon the 

 trap eminences or dikes 

 in and about Ediuburg, 

 on one of which stands 

 the Castle of Ediuburg, 

 compares the work of the denuding agencies to the work 

 of the sculptor, because, as he brings out his figures in 

 alto relievo by chipping away around them, so have these 

 agencies brought out in bold relief the grand trap prom- 

 inences by scooping away the soft shales and sandstones 

 which flanked them. The same can be said of the twin 

 prominences, East and West Rock, that add so much to 

 the scenery about New Haven. Sandstone was all about 

 them, perhaps even covered them, until the sculptor, wa- 

 ter, with its tides, and waves, and currents, removed it. 

 "Trap scenery," remarks Hugh Miller, "may be de- 

 scribed generally as eminently picturesque. From the 

 circumstance that its eruptive masses rise often from 

 amid level fields, and that its hard, abrupt beds, dikes, 

 and columns alternate often with rich, soft strata, that 

 decompose into fertile soils, it abounds in striking con- 

 trasts. The soft plain ascends often at one stride into a 

 hill fantastically rugged and abrupt, and bare and frac- 

 tured precipices overtop terraced slopes or level plat- 

 forms rich in verdure." 



230. How the Trap Rocks were Formed. These rocks 

 were not formed below and then lifted into their places, 

 but, as I have before stated, the material in a molten 

 state was thrust up, and there cooled off and solidified 



