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



Savannah Conglomerate and Sandstone. 



Next in order to the white limestone formation may be mentioned a sand- 

 stone and a conglomerate that rest upon it, and which I have named as above 

 because I have most frequently seen them among- Savannahs. These rocks 

 will be found at the base of the Mocho Mountains (Clarendon), forming the 

 commencement of the large plain of Lower Clarendon and Vere ; St. Jago's 

 Savannah, extending to these mountains, is principally composed of the sand- 

 stone, which is light coloured and friable. From hence the sandstone and 

 conglomerate sweep round by Burnt Savannah to Halse Hall and Hays 

 Savannahs, skirting the white limestone hills and separating them from 

 Diluvium and Alluvium. 



At Halse Hall the conglomerate is composed of rounded pieces of various 

 porphyries and trap rocks, cemented by a dirty white argillaceous substance, 

 and mixed with carnelians, agates, chalcedonies, onyxes, and jaspers. The 

 latter minerals are by no means rare in the conglomerate hill to the south of 

 Halse Hall works (Clarendon). 



In the water-courses among the above-mentioned savannahs there is an 

 abundance of magnetic iron sand : this mineral is indeed common in several 

 parts of Jamaica, but not so much so, I think, as among the savannah sand- 

 stones and conglomerates *. 



The same sandstones and conglomerates will be observed resting upon the 

 white limestone formation in several places on the road from Halse Hall to 

 Old Harbour. These rocks occur in other parts of Jamaica, but in no great 

 abundance in that portion which I have selected for description. 



Diluvium and Alluvium. 



It is gratifying to find Professor Buckland's distinctions so well borne out 

 in a country far removed from those places where they were originally made ; 

 and to see that the same cause, which broke up the surface of European coun- 

 tries, reducing its harder portions into gravel, has also affected Jamaica in a 

 similar manner. The divisions into Diluvium and Alluvium are too well known 

 to require any notice here : I shall therefore proceed to describe those places 

 in Jamaica, where I have observed them. 



The first district which I shall notice is the great plain of Liguanea, upon 



* The beach at the mouth of the Rio Minho (on the left bank) is almost wholly composed of 

 magnetic iron sand, as is also that at the base of the Round Hill in Vere : the same sand is abun- 

 dant on the coast between the Rio Grande and Swift River (north side of the island), and it is 

 frequently found in the water. courses of the Jamaica lowlands; it is not however confined to 

 them; as I have met with it in the mountains. 



