28 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
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 River Basin in northern Manchester, and the Niagara River 
Valley along the boundary of St. Elizabeth and St. James. Moutpelier 
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 tho 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 by 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 Mountains 
rise from 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 longer 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. 
