150 Mr, De la Beche on the Geology of Jamaica. 



The valley of the BufF Bay River affords a somewhat different section of the 

 grauwacke. Ascending the river^ and after passing some red sandstone^ among 

 which porphyritic rocks are seen^ we meet with thick beds- of a brownish red 

 compact sandstone^ mixed with slaty marl^ and very much resembling the old 

 red sandstone of South Wales : this sandstone gradually loses its colour, 

 passes into gray sandstone, and becomes mixed with coarse slate, reminding 

 the observer of the passages of old red sandstone into grauwacke in England, 

 &c. The grauwacke continues for some distance up the river, and then seems 

 gradually to pass into a blueish marly slate (which slightly effervesces) mixed 

 with grayish sandstone (grauwacke) and beds of dark gray compact limestone 

 (traversed by numerous veins of calcareous spar), which latter become more 

 abundant after passing Belcarres. 



The dip of the grauwacke beds on the Buff Bay River is to the N.E. and 

 N.N.E., being the same with the Carlton Wood House beds : this afterwards 

 becomes the nearly general dip of the submedial rocks composing the Blue 

 Mountain Range. 



The Great Spanish and Swift rivers present little or no section of grau- 

 wacke ; the rock which succeeds the red sandstones in those places being 

 principally composed of slaty marl with sandstone, and nodules and beds of 

 compact gray limestone, such as occur beneath the grauwacke on the Buff 

 Bay River. 



The Rio Grande, the next great river to the eastward that cuts the Blue 

 Mountain Range, affords sections of grauwacke closely resembling those of 

 St. Mary's. The road from Port Antonio to Golden Vale is interesting in 

 this respect, as thin beds of grauwacke sandstones intermixed with argilla- 

 ceous slates are there observable dipping from E.S.E. to S.E. 



The higher part of the Cunha Cunha road, between Port Antonio and Bath 

 (St. Thomas-in-the-East) and over the continuation of the Blue Mountains, 

 presents a mixture of brown and gray slaty and compact grauwacke beds, in- 

 terstratified near the summit of the mountain with a conglomerate, in which 

 the rounded pebbles are often of large size, and which evidently belongs to 

 the same series: in fact, the mechanical origin of grauwacke is well exhibited 

 in Jamaica, its beds varying from a fine-grained sandstone to a conglomerate, 

 the pebbles in which are often of considerable size. 



I have observed but little of this rock on the southern side of the Cold 

 Ridge, unless indeed the gray compact siliceous sandstone mixed with slate 

 and thin beds of gray compact limestone, occurring on the northern side of 

 Catherine's Peak, be considered a variety of it. 



Ascending the mountain from the Buff Bay River, which is commonly known 



