SCIENCE. 



gation, 1055 soundings were obtained, of which 35-5 are 

 in depths greater than 1000 fathoms. 



The object of the communication being merely to give 

 a general description of the structural features of the 

 basin of this great inland sea — the American Mediter- 

 ranean — it is only necessary to mention here, that in 

 connection with the soundings, temperatures were taken 

 at various depths, and the organic life was explored by 

 means of dredges. Everywhere below the depth of 

 about 800 fathoms, the temperature was found to be 

 between 39 and 40 F. The method of sounding was 

 by the use .of fine steel wire, indicated by Sir Wm. 

 Thomson, with the mechanical appliances perfected by 

 Commanders Belknap and Sigsbee of the U. S. Navy. 



The exploration of the Gult of Mexico was begun by 

 the U. S. Coast Survey as long ago as 1846, when sur- 

 veys of the shores were made, and soundings of the ap- 

 proacnes were obtained under the Superintendency ot 

 Prot. A. D. Bache. These investigations continued until 

 the outbreak of the civil war, Prof. Bache having in 

 view from the earliest date of his work, the exploration of 

 the Gulf Stream and its attendant phenomena, in addnion 

 to the surveys requisite tor navigation. When alter the 

 close of the war the Coast Survey resumed its former 

 activity, under the administration of Prof. Benjamin 

 Peirce, the physical and biological investigations were 

 continued ; but it was not until the present Superintend- 

 ent of the U. S. Coast Survey, (C. P. Patterson, LL.D.) or- 

 ganized a systematic Exploration of the whole Gulf, that 

 its character became rightly understood. These explor- 

 ations, begun in 1872 by Commander Howell, U. S. N., 

 on the west coast of Florida in comparatively shallow 

 water, were continued and brought to a successful con- 

 clusion by Commander Sigsbee, U. S. N., (1875-78) in 

 the steamer " Blake," accompanied by Prot. A. Agassiz in 

 charge of biological investigations. The methods of ob- 

 taining temperatures at great depths as well as of dredg- 

 ing have been described in the Coast Survey Reports for 

 several years past, and more especially in a treatise by 

 Commander Sigsbee recently published by the Coast Sur- 

 vey. 



Turning now to our model or map, we perceive that 

 the basin of the Gulf of Mexico is an oval connected 

 with the general ocean-circulation by two outlets, the 

 Yucatan Channel and the Florida Straits. The area of 

 the entire Gulf, cutting it off by a line from Cape Flor- 

 ida to Havana, is 595,000 square miles. Supposing the 

 depth ot the Gulf to be reduced by 100 fathoms, a sur- 

 face would be laid bare amounting to 208,000 square 

 miles, or rather more than one third of the whole area, 

 The distance ot the 100 fathom line from the coast is 

 about 6 miles, near Cape Florida; 120 miles along the 

 west coast of Florida ; at the South Pass of the Mississ- 

 ippi, it is only 10 miles ; opposite the Louisiana and 

 Texas boundary, it increases to 130 miles ; at Vera Cruz 

 it is 15 miles, and the Yucatan banks have about the 

 same width as the Florida banks. 



The following table shows the area covered by the 

 trough of the Gulf of Mexico to the depths stated : 



Depth. Area. Differences. 



2,000 fathoms SS.ooo square miles 



1,500 " 187,000 " 132,000 



1,000 " 260,000 73,000 



500 " 326,000 " 66,000 



100 " 387,000 61,000 



Coast line 593,000 208,000 



This table shows that the greatest slopes occur be- 

 tween the depths of 100 and 1500 fathoms. The max- 

 imum depth reached is at the foot of the Yucatan banks 

 21 19 lathoms. From the 1500 fathom line on the north- 

 ern side of the Gulf to the deepest water close to the 

 Yucatan banks, say to the depth of 2000 lathoms, is a 

 distance of 200 miles, which gives a slope of five-ninths 

 to 200, and may be considered practically as a plane sur- 



face. The 2000 fathom area has received the name of 

 "Sigsbee Deep," after its explorer. The Yucatan Chan- 

 nel with a depth of 1164 fathoms has a cross-section of 

 no square miles while the Straits of Florida, in its shal- 

 lowest part opposite Jubiter Inlet, with a depth of 344 

 fathoms has a cross-section of only 10 square miles. 



A view of the model reveals at once some important 

 facts which a study of the plan conveys but imperfectly 

 to the mind, and which were unsuspected before the 

 great exploration of the Gulf was completed. 



Among the more striking features displayed by the 

 model to which Mr. Hilgard called attention, were : 



1. The great distance to which the general slope of the 

 continent extends below the present sea level before 

 steeper slopes are reached. The 100 fathom line repre- 

 sents very closely the general continental line. The 

 massifs of the Peninsulas of Florida and Yucatan have 

 moie than twice their present apparent width. 



2. Very steep slopes lead from this submerged conti- 

 nental plateau to an area as great as that of the State of 

 Georgia at the enormous depth of over 12,000 feet. There 

 are three ranges on the Florida and Yucatan slopes ex- 

 tending in the aggregate from five to six hundred miles, 

 along which the descent from 500 to 1500 fathoms (or 

 6000 feet), is within a breadth of from six to fifteen miles. 

 No such slopes and correspondingly elevated plateaus 

 appear to occur on the un-submerged surface of the earth 

 — the suggestion presents itself, that while the latter have 

 suffered atmospheric erosion, those which we are consid- 

 ering have not sensibly changed from the positions 

 assumed in the mechanical shaping of the earth's crust. 



3. The far protrusion of the Mississipi Delta towards 

 the deep water of the Gulf, seems to give evidence to the 

 Engineer, of the probably permanent success of the 

 Mississippi Jetties, as delivering the silt of the river into 

 water of so great depth that but few extensions will 

 ever become necessary. In connection with the same 

 feature, the strong indentation to the westward of the 

 present mouths ot the Mississippi, indicating the prob- 

 able site of the original fracture between the two slopes 

 of the Mississipi Valley deserves attention. 



4. In regard to the problem of general ocean circula- 

 tion in connection with the Gulf Stream, the most im- 

 portant feature is the shallowness and small cross-section 

 of the Straits of Florida between the Peninsular and 

 Bahama banks, having at the shallowest part a cross- 

 section of 1 1 square miles, with a greatest depth of 344 

 fathoms only. From observations published in the Coast 

 Survey Reports the average northwardly current of the 

 warm water through this Strait is probably not greater 

 than 2 miles per hour— certainly not more than 2.y 2 miles. 

 It is evident, at once, that the warm water which so 

 greatly modifies the climate of Western Europe, cannot 

 all be supplied by the flow through this small channel. 

 The concentration of the warm surface current from the 

 Gulf of Mexico gi ves to this vein of the general circulation 

 a marked velocity, which is not found in other portions 

 of the Atlantic, and which, being perceptible to the navi- 

 gator, has given its name of " Gulf Stream " to the whole 

 system of the northeasterly surface-flow in the Atlantic 

 Ocean. It is now necessary to assume that the so-called 

 Gulf Stream is largely reinforced by a general northerly 

 current from the outside of the West India Islands. 



SCIENTIFIC SOCIETIES OF WASHINGTON. 



The Biological Society. — The Society met in 

 the Smithsonian Institution, Friday evening, March 

 nth, President Gill in the Chair. The discussion 

 was renewed upon Mr. True's paper respecting suc- 

 torial organs. Mr. Seaman spoke of certain plants, 

 such as the American Woodbine, which seem to mimic 

 the suctorial organs of aniriials. Professor Riley drew 

 attention to the suctorial anal pseudopod of caterpillars, 

 and Mr. Goode to the peculiar provision for prehension in 



