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



its surface^ presenting at some distance the appearance of numerous clumps 

 of trees^ distributed over an immense park. These rocky patches are com- 

 posed of compact white limestone^ and the rest of the plain principally of red 

 sandstone ; thus giving to the former the appearance of the remains of conti- 

 nuous strata^ the greater part of which has been swept away. This would in 

 some measure seem the case ; for although the lower limestone strata of these 

 rocky patches are often much intermingled with the red sandstone, and are 

 evidently of contemporaneous formation with it, still the upper strata terminate 

 so suddenly, that there is some reason for beheving that they once extended 

 to a much greater distance than they do at present : thus making it probable 

 that the patches formed continuous strata which have in a great measure been 

 destroyed by denudation, in the same manner as is shown by the larger masses 

 of rock found isolated in other parts of the world. 



These patches may also be accounted for by supposing the white limestone 

 patches to have been included among the red sandstone strata, in the same 

 manner as smaller portions are now seen in the same neighbourhood ; so that 

 when the plains were formed into their present state, the red sandstone, which 

 was softer than the limestone, may be supposed to have given way before the 

 causes which have produced most of the present inequalities in the earth's sur- 

 face, while the limestone was left. I observed that the white limestone beds 

 of many of these patches had a slight dip to the S. W. 



The intimate mixture of red sandstone and white limestone in the neigh- 

 bourhood of New Forest occurs frequently in the same strata, and in such a 

 manner as would make it most difficult to be accounted for except by the 

 theory of contemporaneous formation. There are however other mixtures of 

 the two substances which must have had a different origin, such as the brec- 

 cias and conglomerates in the same district. These are composed of either 

 fragments or rounded pieces of white limestone, but principally of the latter, 

 cemented by red sandstone, or an arenaceous substance of a lighter colour, 

 approaching to yellowish brown, and presenting much the same appearance 

 as the cementing matter of some magnesian or dolomitic conglomerates. It 

 does not however contain any magnesia; for Dr. Daubeny*, to whom I gave 

 specimens for examination, states that " not one of them contains any appre- 

 ciable quantity of magnesia." The pieces of white limestone are so much 

 rounded in the conglomerate, that they appear to have been derived from the 

 forcible destruction of some of the beds by water, anterior to the formation of 

 a considerable portion of the Jamaica white limestone. The red arenaceous 



* Professor of Chemistry at Oxford. 



