Vol. 57.] PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. IxXXlX 



striking exception to the generally received text-book view of 

 the origin of placer gold-deposits. In the speaker's experience 

 the Guiana deposits have not been derived to anj^ great extent from 

 pre-existent quartz-reefs containing gold, but from the degradation 

 in situ of diorites, epidiorites, and hornblende-schists originally 

 more or less auriferous, or in places of mineralized masses and 

 dykes of acidic or of intermediate rocks ; but principally of bosses, 

 sills, and dykes of an intrusive diabase or dolerite of at present 

 unknown geological age, which appear to be always gold-bearing to 

 a minute extent, while in places the selvages of the dykes may 

 contain as much as 5 ounces of gold per ton of the rock. He 

 hoped at some future opportunity to return to the subject, and to 

 lay before the Society the evidence which he had obtained for the 

 above statements, and also the results of many observations bearing 

 on the genesis of placer gold-deposits, and on the concentration of 

 the minute amounts of the precious metal contained in igneous rocks 

 in their degradation-products by processes of chemical solution and 

 redeposition under tropical conditions. 



Finally, he reminded the meeting that the area in which he is 

 at present working forms but a small portion — some 300 miles in 

 breadth — of that great, though almost undeveloped, mineralized 

 belt which extends from El Callao in Venezuelan Guiana to near 

 the mouth of the Amazon in Brazilian Guiana. 



Prof. Edwaed Httll made a communication, illustrated by 

 lantern-slides, on the submerged valley opposite the 

 mouth of the River Congo. The position of this submerged 

 valley has been ascertained by Mr. Edward Stallybrass and Prof. 

 Hull, by contouring the floor of the ocean with the aid of the 

 soundings recorded on the Admiralty Charts. The sides of the 

 valley are steep and precipitous and clearly defined, the width 

 varying from 2 to 10 miles, and the length across the Continental 

 platform being about 122 mUes. It is continuous with the Valley 

 of the Congo, and its slope is uninterruptedly downward in the 

 direction of the abyssal floor. The steepness of the sides indicates 

 that they are formed of very solid rocks. 



Several other submerged valleys ofi' the coast of Western Europe 

 were described for comparison. In most cases the landward end of 

 the submerged river-channel is filled with silt, etc. for some distance 

 from the mouth of the actual river; but, farther out, its course 

 becomes quite distinct towards its embouchure at the edge of the 

 Continental platform. Among the valleys specified were those off 

 the mouth of the Tagus and the Lima, the Adour, and the Loire, and 

 those in the English and Irish Channels. 



The following communication was read : — 



* On the Beds between the Millstone Grit and Mountain Lime- 

 stone of Pendle Hill, and their Equivalents in certain other Parts 

 of Britain/ By Wheelton Hind, M.D., B.S., E.K.C.S., E.G.S., and 

 J. Allen Howe, Esq., B.Sc, E.G.S. 



