Mr. De la Beche on the Geology of Jamaica. 155 



dip towards the sea in that direction : thus the grauwacke between Port An- 

 tonio and the Rio Grande, in the vicinity of Golden Vale estate, dips to the 

 S.E, and E.S.E. ; and some of the beds on the Cunha Cunha road sink to the 

 eastward. 



Trap Rocks associated loith the Submedial Rocks. 



Although it by no means follows that, because trap rocks are associated 

 with submedial rocks, they should be of the same age with them, or formed at 

 the same geological epoch ; yet as a matter of convenience it may be as well 

 to notice here the rocks of this nature, occurring among the submedial rocks 

 of Jamaica, though they very much resemble other trap rocks of the same 

 island, which are connected with a porphyritic conglomerate of more recent 

 formation, to be mentioned in the sequel. That we should not always refer 

 trap rocks to a more distant period of formation than the rocks which appear 

 to rest upon them is well shown in the section afforded by the cliffs near 

 Gouldtrop Road in Southern Pembrokeshire, where greenstone, passing into 

 syenite, rises from beneath old red-sandstone, which seems to rest upon it, 

 although a continuation of the same trap afterwards rests upon contorted car- 

 boniferous limestone and coal measures opposite to the anchorage in Gouldtrop 

 Road : so that the same trap seen at one end of its course might be asserted 

 (judging only from position) to have been formed at a period antecedent 

 to the old red-sandstone ; while, viewed at the other, it might be declared to 

 be a newer formation than the carboniferous limestone and coal measures. 

 So it might happen with the trap of Jamaica, which might easily have been 

 thrown up among the submedial rocks at the same period with the trap occur- 

 ring among the newer rocks ; yet as an abundance of pebbles, evidently de- 

 rived from trap rocks, are found among the red conglomerates which cover 

 the submedial rocks of Jamaica, it is fair to infer that trap must have been as- 

 sociated with these latter rocks previous to the formation of the conglome- 

 rate. There seems, moreover, every reason to suppose that trap rocks, notwith- 

 standing their general similarity of structure, have been formed at distant and 

 distinct periods ; one of these periods seems to have been that when the 

 submedial or transition rocks were formed, and to this period may probably 

 be referred that portion of the Jamaica trap rocks which I am about to 

 mention, though, from the want of good sections, their connexion with the 

 submedial rocks of this island is rather obscure. 



I observed trap rocks in considerable abundance upon the southern side of 

 the Blue Mountain Range ; also upon that portion of it known as the Cold 

 Ridge, and in the highest parts of the Blue Mountain Peak. Ascending 



