HILL: GEOLOGY OF JAMAICxV. 25 



and wide reaching are the influences of sohition that it must be con- 

 stantly considered in a discussion of the region. 



The summit of the plateau is a roughly serrated hilly country, in- 

 dented by cockpits (sinkholes), subcircular basin valleys, and deep drain- 

 ageways leading to the sea. In many places the surface is marked by 

 jagged honeycombed rocks, between which grows a dense tropical foliage. 

 Knife-edged lateral salients, like those which characterize tlie Central 

 Mountains, are missing from this topography. Steep bluffy, undermin- 

 ing benches, caverns, and sinkholes abound. 



The Cockpit Country. — The origin of the ragged summit topography 

 of the White Limestone Plateau, and the evolution of the numerous in- 

 terior basin valleys of which they are antecedent, can be best illustrated 

 by a description of " the cockpit country," as it is locally called ; this, 

 with its modifications, includes the whole of the high interior portions 

 of the parishes of St. Ann, Trelawney, St. James, Hanover, Westmore- 

 land, Manchester, and St. Elizabeth, to the west and north of the 

 Clarendon ridges, although the cockpits are limited to a rough district 

 embracing the corners of Trelawney and St. James. In the interior of 

 the western half of the island the hills are sharply rounded conical 

 points. Towards the coast there are long flat-topped ridges with steep 

 slopes, such as the John Crow Eidge of Portland, Yallahs Ridge of St. 

 Thomas, Long Mountain of St. Andrew, the Healthshire Hills of St. 

 Catherine, the Portland Hills of Clarendon, and others. Still another 

 type are flat-topped circular mesas with steep walls, such as occur in 

 parts of Westmoreland and Hanover. 



The cockpits are primarily deep funnel-shaped sinkholes, from which 

 the drainage percolates downward into the cavities and fissures of the 

 underlying rocks. The steep acclivities of these holes ascend into 

 pointed conical hills. Their origin and evolution is shown upon the 

 accompanying figure. The pits vary in depth from shallow circular 

 basin-like depressions surrounded by low mammillary hills (Fig. 7, i) 

 which mark the youthful stage of their formation, to deep-sided sinks 

 often 500 feet in depth, denoting the acute stage of development (Fig. 7, ii). 

 Both these types are common on the summit region, where there is no 

 surface drainage, the water settling in pools and penetrating down into 

 the soluble and open textured substructure, carrying with it lime in 

 solution and leaving behind as soil and in the cavities of the limestone 

 a blood red residuum of iron and clay, as may be seen in many fine 

 vertical sections cut along the line of the newly constructed Montego 

 Bay Railway. 



