Vol. 58.] GEOLOGICAL DEVELOPMENT OF DOMINICA, ETC. 341 
20. On the Guotocrcat and Puystcat Drevetopment of Dominica ; 
with Notes on Martiniquet, Str. Lucra, Sr. Vincent, and THE 
Grenapines. By Prof. JossepH Witt1am WintHrop SPENCER, 
M.A., Ph.D., F.G.S. (Read December 18th, 1901.) 
[Prats X—Map.| 
ContTENTS. 
Page 
I. Introduction ........ Botanic: iye baa.cleite cn sryaltih aia estamos Wide ome hn isigtaaletle 341 
II. Situation and Hydrographical Characteristics ..................... 341 
MEP hysical” CHAracherist Gs a. ccc 5 sete oso cnign a cnteseo eyes madarsncstetns 345 
IV. The Volcanic Formations of Dominica....... Sievers Seater ae ae ery 347 
We The Gravel-Kormations of Dominica: ... 2.2.0.0. setcectenessvcnees 348 
VI. On the Coral-Point Formation and the Age of the Gravels...... 349 
BR Wee REETACES Sof. 2 ois. (ccein de 2 s.5au age tasigcltioncns= Nop qoameonnanorews eases 350 
VIII. Notes on Phenomena repeated in the Islands South of Dominica. 351 
Mie summary and, Conclusions: 65.5.5. ss. oes eeeclenac comers Neeser vette, 352 
I. Inrropvuction. 
THe features of this chain of islands form a striking repetition, or 
rather interrupted continuation, of the mountainous portions of 
Guadeloupe and Antigua—in a word, they are largely made up of old 
igneous formations, the surfaces of which have been greatly denuded, 
surmounted by the more recent volcanic accumulations, some of 
which rise into high mountain-peaks. The general geological and 
physical history, with local variations, is repeated to such an extent, 
that these islands can only be regarded as one physical unit. 
The only paper that I have seen upon the geology of Dominica is 
that entitled ‘ Notes of a Visit to Dominica’ by Mr. R. J. Lechmere 
Guppy.’ There are also some scattered references to the late volcanic 
eruptions of the various islands; but this is not the subject of our 
investigations. Outside of Dominica, my personal observations were 
made at only a few points, where the older volcanic foundations 
alone were seen, modified by atmospheric agents; these showed, 
however, a repetition of the features of Guadeloupe and Dominica. 
II. Srrvation anp HyproGRaPHICAL CHARACTERISTICS. 
Dominica is separated from the Guadeloupe archipelago by a 
depression in the Antillean plateau from 15 to 20 miles wide,” 
which is submerged to about 2100 feet (see map, Pl. X). This 
depression is indented by an ‘embayment extending within the 
line connecting the western shores of Guadeloupe and Dominica, 
where even the few soundings reach 1200 feet deeper than those 
on the surface of the ridge. Martinique is 25 miles distant from 
the southern end of Dominica, but the submarine features already 
* Proce. Sci. Assoc. Trinidad, Dec. 1869, pp. 377-92, with two plates. 
* See U.S. Hydrographic Chart No. 40, or the British Admiralty equivalent. 
Q.J.G.8. No. 231. 2B 
