Nov. II, 1 886] 



NA TURE 



Z2> 



In concUision, it ought to be stated that this brief 

 review of the Charleston earthquake must be regarded 

 only as an attempt to place some of the leading facts 

 upon record, for the benefit of the readers of the Montlily 

 Weather Revieic. It is in no way intended to anticipate 

 the investigations now in progress by the United States 

 Geological Survey, a full report from which, based upon 

 all attainable information, will be looked for with great 

 interest. 



THE SIMILARITIES IN THE PHYSICAL 



GEOGRAPHY OF THE GREAT OCEANS^ 

 A T the outset Mr. Buchanan reminded the audience 

 ■^*- of the similarities observed in the eastern and 

 western continents, especially in their southern extremi- 

 ties. Such similarities in corresponding localities had 

 been called homologous geographical features, in imitation 

 of the homologies of comparative anatomy, and they had 

 received much attention from students of geography. A 

 remarkable group of similarities of this kind is to be 

 found in the arrangement of inclosed seas lying to the 

 northward of the three southern continents. To the 

 northward of South ."Xmerica there are the Gulf of 

 Me.xico and the different basins of the Caribbean Sea ; to 

 the northward of Africa there are the Mediterranean with 

 its different basins, and on the north-east the Red Sea ; 

 and to the northward of Australia there are the well- 

 known seas of the Eastern Archipelago. These seas are 

 bounded on all sides by islands and insular groups, and 

 they are in continuous connection with two oceans, the 

 Pacific and the Indian. The African seas are bounded 

 entirely by continental land and communicate directly 

 with tuo oceans ; but in the limited sense that one sea, 

 the Red Sea, communicates with the Indian Ocean by a 

 single channel, and the Mediterranean Sea with the 

 Atlantic, likewise by a single channel. Finally, the 

 American seas are all in continuous communication with 

 only one ocean, the Atlantic, the continental barrier 

 towards the Pacific being continuous. 



It is not unworthy of remark that the great depths 

 (over 4000 fathoms) of the Atlantic and the Pacific Oceans 

 occur immediately to the northward of these groups of 

 seas, and in the western sinus of the northern portions of 

 both oceans ; while the greatest depression of the con- 

 tinental land, the region of the Dead Sea, is found similarly 

 situated with regard to Africa. The analogy here, how- 

 ever, does not hold good all through, because it is a mere 

 accident of climate that this area does not form a large 

 and not excessively deep fresh-water lake. 



The seas of the Malay .^Archipelago and those of the 

 West Indies have important functions in the physical 

 geography of the oceans, as they receive the warm dense 

 water of the westerly-running equatorial currents of the 

 Pacific and the Atlantic Oceans. The Pacific current 

 finds no obstacle in the chains of islands which bound the 

 Malayan seas, and is able to pass freely through into the 

 Indian Ocean ; while the Atlantic current is stopped by 

 the continuous continental barrier of South America, and 

 the head of water thus produced is relieved by the over- 

 flow of the Gulf Stream all the year round. Although 

 there is no static barrier, in the shape of continuous land, 

 to the westerly Pacific current, there is, during one season 

 of the year, a kinetic one, furnished by the prevalence of 

 the south-west winds during the monsoon season. These 

 furnish the intermittent kuio siwo. The main cause of 

 the westerly equatorial current is the propulsive action 

 of the trade winds. 



These winds have also great evaporating power ; and, 

 by making the surface water Salter, they furnish the 

 mechanical means of propagating the surface heat into 

 the deeper layers of the ocean. Hence the leading cha- 



' Abstract, by the A 

 Geographical Society t 



t the meeting of the Royal 

 , by Mr. J. Y. Buchanan. 



racteristic of the westward or leeward regions of the 

 intertropical oceans is water of considerable density and 

 of high average temperature in the sub-surface layers. 

 This characteristic is seen most clearly in the Atlantic, 

 where there is no communication with another ocean. In 

 the Pacific the non-continuous boundary neutralises to 

 some extent this effect, and gives to the eastern parts of 

 the Indian Ocean a borrowed leeward character, inde- 

 pendent of its own climate. A secondary consequence of 

 a leeward position in the ocean, and due to the above- 

 mentioned characteristics of the temperature and density 

 of such water, is the prevalence of coral formations in the 

 western regions of the Atlantic and Pacific, and, owing to 

 the mixture of conditions, in both eastern and western 

 regions of the Indian Ocean. 



Continental homologies, or similar features in corre- 

 sponding localities, are found on the western as well as 

 on the eastern sides of the continents. One of the most 

 striking is the resemblance of the Gulf of Guinea on the 

 African coast with the great Central American bight 

 stretching from Cape St. Lucas at the extremity of the 

 Californian Peninsula, by Panama, to the mouth of the 

 Guayaquil River, and with the unnamed bight in the 

 Indian ocean bounded continentally by the north-west 

 coast of .'Australia and insularly by the chain of islands 

 stretching from the Peninsula of Malacca to Australia. 

 Oceanically these bights are homologous. It is in them that 

 the beginnings of the westerly-running equatorial currents 

 are to be found, and perhaps more important still, it is in 

 them that the easterly-running counter equatorial currents 

 end. They are to be found in each of the three oceans, 

 and generally on the northward side of the axis of the 

 westerly-running current. In the Atlantic it is best known 

 by its eastern portion, the Guinea current. 



The observations here recorded of the Guinea current, 

 a hitherto unexplored region of the ocean, were made on 

 board the steamship Buccaneer, at the invitation of the 

 owners, the India-rubber, Gutta-percha, and Telegraph 

 Works Company, of Silvertown, and were carried out 

 during a survey for a telegraph cable from Sierra Leone 

 to St. Paul de Loanda. From a diagram showing the 

 variation of salinity of the surface water of the Guinea 

 current, with distance from the coast, it appeared that for 

 a considerable distance along the Guinea coast the salinity 

 of the surface water was an almost accurate test of the 

 pro.ximity of the land. The Guinea current starts in mid- 

 ocean, but it is most constant near the African coast. The 

 density of the water is low, its temperature high, and its 

 velocity, especially in-shore, is sometimes as great as 

 three miles an hour. It varies somewhat with the 

 season. 



Bottle experiments showed an average rate of fifteen 

 miles per day in the months of January and February, 

 for a thousand miles along the coast. In March, the .5 ;^c- 

 caneer experienced no easterly current, and in connection 

 with this absence of easterly currents off the coast maybe 

 taken the very remarkable under-current which is found 

 setting in a south-easterly direction with a velocity of over 

 a mile per hour at three stations almost on the equator, 

 and, to the northward of the Island of Ascension. For 

 the double purpose of examining the currents and of 

 obtaining a large specimen of the bottom, the Buccaneer 

 was anchored in 1800 fathoms of water by means of an 

 ordinary light anchor fitted with a canvas bag to receive 

 the mud which would otherwise fall off the flukes on its 

 being weighed. While the ship was lying thus at anchor, 

 the surface water was found to have a very slight westerly 

 set. At a depth of 15 fathoms there was a difference, 

 and at 30 fathoms the water was running so strongly to 

 the south-east, that it was impossible to make observations 

 of temperature, as the lines, heavily loaded, drifted straight 

 out, and could not be sunk by any weight the strain of 

 which they could bear. In the Pacific the counter equa- 

 torial current in the open ocean was well observed by the 



