28 bulletin: museum of compaPwATIye zoology. 



many cases these valleys have no superficial outletting drainage, while 

 in others the barriers have been partially eroded away, and they are 

 drained by rivers leading to the sea. 



The largest of these depressions are those of St. Thomas-in-the-Vale, 

 the great Vale of Clarendon, surrounding the Clarendon Mountains, the 

 Hector liiver Basin in northern Manchester, and the Niagara River 

 Valley along the boundary of St. Elizabeth and St. James. Montpelier 

 Valley along Great River in Hanover, and Morgan's Gut Valley in 

 Westmoreland, are similar basins which have had drainage gaps cut 

 through their surrounding barriers. The latter now constitutes an in- 

 terior embayment of the great plain of Savanna-la-Mar. 



The valley of St. Thomas-in-the-Vale is almost circular in outline 

 and its floor has a diameter of ten miles. Its bottom is largely covered 

 with old alluvium. The mountainous scenery encircling this basin is 

 beautiful beyond description. From Ewarton can be seen a band of 

 white limestone, rising on the west side of the valley in a gentle arch, 

 and extending for miles towards Moneague. This band has a steep 

 face, and is crested by rugged points forming the plateau summit. The 

 culmination of this arch is Mount Diablo, whose summit is 2,500 feet 

 above the bottom of the basin. This valley is drained by about ten 

 copious streams, which gather into a single arterial trunk, the Rio Cobre, 

 by which they pass to the sea through the narrow gorge of Bog Walk 

 Canyon. These streams have their sources in springs or caverns in 

 lower portions of the limestone formation of the hilly perimeter near 

 their contact with the impervious Blue Mountain Series. At one 

 time in its history this valley had no direct outlet to the sea, but con- 

 nection has been made by encroachment upon the divide b}' the former 

 headwaters of the Rio Cobre, which was originally a simple marginal 

 coastal stream, and its capture of the basin drainage. 



The Clarendon Valley has been partially described in our remarks on 

 the Clarendon Mountains. While this is of the same general type and 

 origin as that of St. Thomas-in-the-Vale it differs from it in details of 

 configuration, chief of which is the fact that the Clarendon ^fountains 

 rise fi'om its centre so that the valley proper is confined to an annular 

 area lying between these mountains and the surrounding white lime- 

 stone escarpments. The Clarendon Valley is about 50 miles in length 

 and 25 miles in width. Its lonjzer direction corresponds with that 

 of the axis of the plateau. The drainage, like that of St. Thomas-in- 

 the-Vale, concentrates into an arterial trunk known as the Minho, 

 through the canyon of which it outlets to the south coast. 



