284 



NATURE 



[January 21, 1892 



trees, to the description given of them by Darwin, who repre- 

 sents them in the height of the dry season as the supreme 

 expression of desolation and barrenness. Of course, here and 

 there were extensive tracts on the sea-shore where there was 

 nothing to be seen but bloci<s of volcanic ashes, with an 

 occasional cactus standing in bold relief, or a series of mud 

 volcanoes, or a huge black field of volcanic rocks, an ancient 

 flow from some crater to the sea ; but as a rule the larger 

 islands presented wide areas of rich fertile soil, suitable for 

 cultivation. The experiments at Charles Island, where there 

 is a deserted plantation, and at Chatham Island, where Mr. 

 Cobos has under successful cultivation a large plantation pro- 

 ducing sugar, coffee, and all the tropical fruits, as well as 

 extensive tracts on which his herds of cattle, sheep, and donkeys 

 roam towards the higher central parts of the island, show the 

 fertility of these islands. They are indeed as favourably situated 

 for cultivation as the Sandwich Islands or Mauritius, and there 

 is no reason why, if properly managed, ihey should not in the 

 near future yield to their owners as large returns as do those 

 islands. 



I obtained from Mr. Cobos a piece of the so-called sandstone, 

 said to occur on Indefatigable Island, and which of course I 

 was most anxious to see, as the occurrence of true sandstone 

 would have put quite a different face on the geological history 

 of the Galapagos from the one usually received. This I found 

 to be nothing but coral rock limestone, either a breccia, or 

 slightly oolitic, identical with the formation found back of the 

 beach at Wreck Bay on Chatham Island. I found there an old 

 coral rock beach, extending on the flat behind the present 

 beach, composed entirely of fragments of corals, of moUusks, 

 and other invertebrates, cemented together into a moderately 

 compact oolitic limestone, which when discoloured, as it often 

 is, and turned gray, would readily be mistaken for sandstone. 

 This coral rock is covered by just such a thin, ringing coating 

 of limestone as characterizes the modern reef rock of other 

 localities. On nearly all the islands there are a number of 

 sandy beaches made up of decomposed fragments of corals and 

 other invertebrates, and cemented together at or beyond high- 

 water mark into the modern reef rock I have described. The 

 coral is mainly made up of fragments of Pocillopora, which is 

 found covering more or less extensive patches off these coral 

 sand beaches, but which, as is well known, never forms true 

 coral reef in the Panamic district. The only true coral reef 

 belonging to this district is that of Clipperton Island (if we can 

 trust the Admiralty charts), situated about 700 miles to the 

 south-west of Acapulco. But neither at Cocos Island, nor at 

 the Galapagos, nor anywhere in the Panamic district, do we 

 find true coral reefs — nothing but isolated patches of reef- 

 building coral. The absence of coral reefs in this district has 

 of course already been noted by other naturalists, who have 

 been struck by this feature in an equatorial region. Dana has 

 ascribed it to the lower temperature of the water due to the 

 action of the Humboldt current coming from the south, pouring 

 into the Bay of Panama, and then flowing westward with the 

 colder northerly current coming down the west coast of Mexico 

 and Central America. From the investigations made this year by 

 the Albatross, I am more inclined to assume that the true cause 

 of the absence of coral reefs on the west coast of Central 

 America is due to the immense amount of silt which is brought 

 down the hill and mountain sides every rainy season, and which 

 simply covers the floor of the ocean to a very considerable dis- 

 tance from the land, the land deposits being found by us even 

 on the line from the Galapagos to Acapulco at the most distant 

 point from the shore to the side or extremities. The mud in 

 Panama Bay to the hundred-fathom line is something extra- 

 ordinary, and its influence on the growth of coral reefs is un- 

 doubtedly greatly increased from the large amount of decomposed 

 vegetable matter which is mixed with the terrigenous deposits. 



The course of the currents along the Mexican and the Central 

 and South American coasts clearly indicates to us the sources 

 from which the fauna and flora of the volcanic group of the 

 Galapagos has derived its origin. The distance from the coast 

 of Ecuador (Galera Point and Cape San Francisco) is in a direct 

 line not much over 500 miles, and that from the Costa Rica 

 coast but a little over 6co miles, and the bottom must be for its 

 whole distance strewn thickly with vegetable matter. The 

 force of the currents is very great, sometimes as much as 75 

 miles a day, so that seeds, fruits, masses of vegetation harbouring 

 small reptiles, or even large ones, as well as other terrestrial 

 animals, need not be afloat long before they might safely be 



NO. II 60, VOL. 45] 



landed on the shores of the Galapagos. Its flora, as is well 

 known, is eminently American, while its fauna at every point 

 discloses its affinity to the Mexican, Central or South American, 

 and even West Indian types, from which it has probably origin- 

 ated ; the last indicating, as well as so many of the marine types 

 collected during this expedition, the close connection that once 

 existed between the Panamic region and the Caribbean and Gulf 

 of Mexico. 



I have already referred to the physiognomy of the deep-sea 

 fauna, showing relationship on the one side to Atlantic and West 

 Indian types, and on the other to the extension of the Pacific 

 types, which mix with the strictly deep-sea Panamic ones. 

 The western and eastern Pacific fauna, while as a whole pre- 

 senting very marked features in common, yet also present 

 striking differences. The vast extent of territory over which 

 some of the marine types extend, through all the tropical part 

 of the Pacific, may readily be explained from the course of the 

 great western equatorial current and the eastern counter current, 

 which cannot fail to act as general distributors in space for the 

 extension of a vast number of marine Vertebrates and In- 

 vertebrates. 



Mr. Townsend made quite a large collection of birds from 

 Chatham and Charles Islands, considering the short time we 

 were there. 



As soon as we have reached Guaymas, I shall be able to give 

 you a better resume of the character of the deep sea fauna of the 

 Panamic region, and of its relationship on the one side to the 

 Pacific fauna and on the other to the West Indian region. 



III. 



Guaymas, April 25, 1 89 1. 

 We left Acapulco on April 15 for our third cruise into the 

 Gulf o' California, and steamed as far as Cape Corrientes with- 

 out attempting to do any trawling. The character of the bottom, 

 as indicated on the charts, promised nothing different from what 

 we had dredged off Acapulco, and on the line from there to the 

 Galapagos Islands. We made one haul off Cape Corrientes, 

 brii^ing up nothing but mud and decomposed vegetable matter. 

 This induced us to keep up the Gulf of California till we were 

 off the Tres Marias. We there made several hauls, and ob- 

 tained some UmbellulK, Pennatula, Trochoptilum, Antho- 

 ptilum, and a fine Antipathes, a few Comatulae, a large Astro- 

 pecten, some fine specimens of Urechinus and of Schizaster, a 

 few Holothurians, Lophothuria, Trochostoma, and two species 

 of Elasipoda, besides a few fragments of Gasteropods, with an 

 empty shell of Argonauta. 



Among the Crustacea there came up the usual types found 

 living upon muddy bottom, such as Glyphocrangon, Hetero- 

 carpus, Notostoma, Pentacheles, Nematocarcinus, Nephrops, 

 together with species of Lilhodes and of Munida. The usual 

 types of Limicolous Annelid also were found here, Halinsecia, 

 Terebella, Maldania, and the like, a few Ophiurans, Ophio- 

 pholis, and Ophiocantha, a few fragments of Farrea, and a huge 

 Hyalonema ot the type of //. toxeres. Among the Fishes there 

 were a few Macrurans, Bathypteroides, Lycodes, and Malthe. 

 The trawl was usually well filled with mud, and with the mud 

 came up the usual supply of logs, branches, twigs, and decayed 

 vegetable matter. 



On going farther north into the Gulf of California, the nature 

 of the bottom did not change materially, and we found the 

 trawling most difficult from the weight of the mud brought up 

 in the trawl. But occasionally a haul was made which more 

 than repaid us for the time spent on the less productive ones. 

 Two of the hauls are specially worthy of mention, as being cha- 

 racteristic of the deep-water fauna of the Gulf of California, one 

 made in 995 fathoms, and the other in 1588 fathoms. We ob- 

 tained in these hauls a number of Ophiomusium and Ophiocreas, 

 some fine specimens of Schizaster, a new genus allied to Palaeo- 

 pneustes, and also the same species of Cystechinus, with a hard 

 test, and of Phormosoma, which we had obtained before on 

 the line from the Galapagos to Acapulco. Beside these there 

 came up a number of specimens of an interesting species of 

 Pourtalesia, most closely allied to Pom-talesia miranda, the first 

 type of the group dredged in the Florida Channel by Count 

 Pourtales. 



The deeper haul was specially rich in Holothurians, among 

 them a fine large white Cucumaria, some specimens of Trocho- 

 stoma, several species of Bathodytes, some of them remarkable 

 for their white colour, their huge size, and comparatively small 



