Vol. 58.] GEOLOGICAL DEVELOPMENT OF DOMINICA, ETC. 345 
Other large embayments indent the western margin of the 
Grenadines. By a careful study of the more complete chart,’ the 
heads of several of the smaller amphitheatres, of a mile or less in 
breadth and a mile or two in length, are seen indenting the drowned 
plains to depths of 600 to 900 feet, such as that at Kingstown in 
St. Vincent and that south-east of Carriacou, one of the Grenadines. 
Small channels are often observable on the surfaces of the sub- 
marine plains having depths of 50 to 100 feet, recording the late 
erosion when the marine banks formed land-features. 
Such valley-like features are constantly recurring in the sub- 
marine plateau throughout the group. ‘They are better shown 
on their western side than upon the eastern, where even the 
scantier soundings show that the descent is more precipitous. From 
a study of the indentations, which are the exact reproduction of 
the amphitheatres or cirques, or somewhat longer valleys, upon the 
margins of the tablelands of Mexico, one is impelled to the conclusion 
that these submarine features were modified, if not formed, by sub- 
aérial denudation, when the land stood as high as the valleys are now 
depressed—in other words, at least 6000 or 7000 feet higher than 
now; while the small channels seen on the surface of the banks 
were formed at a later date, when the land was not more than 200 
feet or so above the sea. 
Tlf. Puysicat CHARACTERISTICS. 
Dominica. 
This island has an elliptical form, with a maximum length of 54 
miles and a breadth of 15. It is the most completely mountainous 
of all the islands, and consists of a mass of volcanic ridges dissected 
by deep gorges. The highest point is Morne Diablotin, 4747 feet, 
aud the Trois Pitons reach to nearly the same altitude. The Grande 
Soufriére (3554 feet above sea-level) was in eruption in 1880. The 
flanks of the mountains are characterized by slopes caused by the 
tilting outward of great beds of stratified tuffs, which are dissected 
by deep valleys, between which are numerous isolated peaks. 
There are no coastal plains of importance, the only flat land being in 
the lower reaches of the short valleys, as that of the Layou River, or 
on fragments of low terraces. There is even no other submerged 
coastal plain, than a small fragment on the eastern or north-eastern 
side, which does not reach a width of 4 miles (see Pl. X). This 
margin is seen to be dissected by channels, one of which, south-east 
of Rosalie, reaches to a depth of 600 or 700 feet, where the shelf is 
covered by only 200 feet of water. 
Among the mountains, many fragments of base-levels of erosion 
are observable, as at Bona Vista, at the head of the Roseau 
valley, and also at the divide along the road between Roseau and 
Geneva, at elevations of 1500 to 1700 feet. One at 500 feet above 
the sea was quite extensive, and another at an altitude of between 
1 U.S. Hydrographic Charts Nos. 1279 & 1640, ete. 
