10 BULLETIN OF THE 
general depth between them and the mainland. This flat floor also 
extends farther to the southeast towards the 1,500 fathom line from 
which the Galapagos rise begins, and in the direction of the Costa Rica 
coast. The slope from the 1,000 fathom line to the 1,500 and 2,000 
fathom line is much more gradual between Costa Rica and Tehuantepec 
than farther north along the coast of Mexico as far as the Gulf of Cali- 
fornia (Plate IIT.). 
Our knowledge of the hydrography of the Galapagos is still quite in- 
complete. (See Plates IV. and VIII. to XII.) There are unfortunately 
no soundings between James and Albemarle, or between Indefatigable and 
Albemarle, to indicate the probable depth of the ridges connecting them. 
Nothing likewise is known of the depth of the channels between 
Abingdon and Bindloe and’ Tower, and no soundings exist to show 
how far to the westward the deep valley (of over 800 fathoms) separat- 
ing Bindloe from Indefatigable extends (Plate X. Fig. 2), as there are 
no soundings between either Bindloe or Abingdon and Albemarle. 
There seems little doubt that the northernmost islands, the isolated 
rocks of Culpepper and Wenman, are themselves separated by com- 
paratively deep water (Plate XII. Figs. 1, 2), and in turn separated 
from the northeastern group of islands, Abingdon, Bindloe, and Tower, by 
a tongue of the ocean of at least 1,000 fathoms in depth, and from sixty 
to seventy miles in width. From a careful examination of the soundings 
thus far made, it seems probable that the 100 fathom line connects 
Indefatigable, Duncan, Barrington, and Charles, (see Plate IV., as well 
as the line between Charles and Indefatigable, Plate XI. Fig. 1,) and 
that there is also a connecting ridge inside that same depth between 
those islands and Albemarle to the southeast of Cape Woodford on 
Albemarle, or a wider plateau of which Duncan Island is one of the 
culminating summits. 
A comparatively shallow connection may also exist between Cape 
Nepean on James Island and Albemarle in the direction of Cowley 
Island, Narborough itself being only separated from Albemarle by a 
channel less than 75 fathoms in depth (Plate IV.). The soundings be- 
tween Chatham, Barrington, and Hood are so few in number that we are 
not yet able to decide whether these southeastern islands, Chatham and 
Hood (Plate XI. Figs. 2, 3), are not perhaps connected by a ridge con- 
necting Hood and Macgowen Reef (Plate IV.), and also uniting them 
with the great plateau which the islands of Barrington, Charles, Inde- 
fatigable, Duncan, Albemarle, Narborough, and perhaps James, have 
gradually built up. But it may be that the tongue of deeper water 
