Mr. De la Beche on the Geology of Jamaica. 149 



Bay. Upon the Swift^ Great Spanish, and Buff Bay rivers these rocks will 

 be observed separated from the white limestone formation by red sandstone. 



The following rocks constitute this sub medial country. 



Grauwacke. — This rock is well exposed in St. Mary's, and varies in its 

 structure from a fine-grained compact sandstone to a coarse conglomerate, 

 both occurring in beds of various thickness and occasionally interstratified 

 with grauwacke slate of various degrees of fineness. The colour of this rock 

 varies from gray to brown ; the conglomerate contains portions of quartz, 

 syenite, &c. from the size of a nut to three or four inches in diameter. 



The road from Forster's Cove to Port Maria affords several fine sections of 

 slaty and compact grauwacke *; the inland road from Port Maria to Islington 

 estate does the same, more particularly near Quebec estate, between which 

 place and Port Maria there is a good exhibition of the compact variety in 

 thick beds. The strata of this district, though they sometimes undulate, and 

 therefore have the appearance of inclining in contrary directions, dip gene- 

 rally to the S.W. at angles varying from 30° to 50°. There are, however, 

 some thick conglomerate beds, which though of rather an ambiguous charac- 

 ter, more resemble the grauwacke conglomerate of Jamaica, than any other 

 rock which I observed in the island ; these dip to the N, at Forster's Cove. 

 Between the latter place and Islington, thin beds and nodules of compact gray- 

 ish blue limestone occur among the grauwacke rocks. Near Albion estate, 

 not far from Port Maria, compact sandstone beds, which appear to belong to 

 the grauwacke series, will be observed, and between that place and Eden 

 estate I found a compact sandstone with vegetable impressions ; these were 

 however but ill defined, and had the appearance of reeds, not of ferns. Large 

 blocks of porphyry, with a dull green and rather earthy base containing white 

 crystals of felspar and small grains of quartz, are found at Stony Cove : this 

 rock would seem to be associated with the grauwacke. 



The grauwacke beds on the coast at Carlton Wood House, a short distance 

 eastward from Forster's Cove, dip at a considerable angle to the N.E., but at 

 Agualta Vale Pen, under the hill upon which the house stands, is afforded a 

 section of slaty and compact grauwacke beds, dipping at about an angle of 

 40° to the S.W. ; so that the strata would appear to be arched between these 

 two places, the latter of which is situated about five miles in a S.S.E. direc- 

 tion from the former. 



Proceeding from Agualta Vale Pen up the Agua Alta, grauwacke occasion- 

 ally composed of very thick beds of coarse conglomerate will be observed for 

 some distance up the picturesque valley in which the river flows. 



* A variety of grauwacke sandstone from Forster's Cove effervesces slightlvi. 



