552 DEEP-SEA DEPOSITS. 



may be foriued of it as if the bottom were not concealed from us by the 

 covering of water above. Such is specially the case for the Straits of 

 Dover. 



Thome de Gamond, who was the initiator of the proposal to make a 

 tunnel across the English Channel, saw the necessity of hrst malcing a 

 Study of the submarine ground.* Altliongh he had onl^- his own personal 

 resources and was un})rovided with any diving apparatus, the projector 

 of this attempt, with a boldness wliicli j)roveshis excessive enthusiasm 

 for his idea, did not hesitate to launch himself into the sea in a strange 

 apparatus of his own invention. After diving with great intrepidity 

 three times in one day, he managed to acMjuire usefnl data for a distance 

 of a kilometer and a half from the shore. 



Later, Avhen the same problem came to be studied in a more exact 

 manner, the necessity of a basis of absolutely exact data was perceived. 

 First of all, it was necessary to determine upon the sea bottom the con- 

 tinuity of the different strata of the cretaceous formation, which appear 

 very much alike in both the French an<l English cliff's on both sides of 

 the channel. A commission composed of Messrs. Larousse, Potier, and 

 Lapparent made 7,(»00 soundings, of which nearly 3,000 returned deter- 

 minable si)ecimt'ns. Thus, thanks to geology, the enterprise which at 

 tirst appeared so doubtful, rested hencefortli upon positive facts ac(;u- 

 rately established. It was learned that the boring could be continuously 

 carried on in a layer of so-called (jrey cliall' soft enough to be easily 

 worked, ami snfliciently impervious not to allow the penetration of 

 water. 



Lastly, and <piite recently, after having been forced to abandon a 

 sub-marine passage, it was suggested to build a bridge across the straits 

 of Dover. The bottom of the channel was again made the object of 

 numerous careful investigations. This time the nature of the ground 

 upon which the jnles would rest had particularly to be known. The 

 exploration made in 1890 by Mr. J. lienanlt, hydrographic engineer, 

 furnished the data, and in addition to the usual material for sounding 

 and diedging, he constructed special apparatus for drilling which was 

 used. Four hundred drillings were made, and not fewer than 3,000 

 soundings. 



The marginal sediments of which we have just spoken, and to which 

 Messrs. Murray and llenard give the name terrigenous, extend along 

 the continents, over a zone which, measured from the shore, occupy the 

 variable dimensions of from 10!J to 500 kilometers. They also form the 

 bottom of inland seas, such as the Mediterranean, the seas of North 

 China, of Japan, and of the Antilles. 



Besides the marginal deposits that we have just mentioned, and the 

 deposits of the great depths which we are about to consider, there 



* Thome cle Ganioiid. Shidy for a proposed submarine tunnel between England and 

 France, unitinrj the railwii>i-s of the two countries without breakiuf/ bulk, by the line of 

 Grinez to Eastirare, irith map of proposed dirceliou and the profile of the tunnel crossing 

 the geological diagram of the subnierged pier. 4to. Paris, 1857. 



