562 Notices of Memoirs — The Britinh Association. 



are not agitated by large streams bearing earthy sediments during 

 times of freshets, the deposits generally consist of a light slimy 

 brownish mud sometimes of a depth beyond twenty feet, into which 

 a pole can be easily driven by the hand. This mud, when ti-eated so 

 as to eliminate the carbonaceous vegetable matter, leaves a variable 

 percentage of exquisitely sculptured diatom cells and various forms 

 of sponge spicules. In some places this percentage is very high and 

 the deposit cori-espondingly whiter and firmer, in some cases consist- 

 ing nearly of the pure siliceous valves and spicules. The DiatoinacesB 

 grow not only in the waters of these lakes, but in the streams flowing 

 into them, so that these deposits are not all developed in situ. The 

 sponges, on the other hand, affect the stiller waters of the lake. 

 They attach themselves to and grow upon portions of submerged 

 wood, stone or even sand, sometimes forming extensive incrustations 

 several inches in thickness, some species extensively lobed and even 

 branching. The sponge-flesh dying away each winter, innumerable 

 microscopic spicula which formed its skeleton are thus scattered in 

 the waters, so that in some localities the sponge spicules form a 

 greater proportion of the deposits than the valves of the Diatomacese. 



Some of these deposits may prove to be of industrial importance, 

 the material being regarded as capable of use as polishing powder 

 for various purposes, and in the manufacture of dynamite. 



The lakes upon which these preliminary observations have been 

 made include Ainslie, in Cape Breton ; Lochaber, in Antigonish Co. ; 

 Mackay, Blackbrook, Garden of Eden, Grant, M'Lean, Calder, 

 Forbes, Ben, and Toney Lakes in Pictou Co. ; Mackintosh, Earltown, 

 and Gulley Lakes, in Colchester Co, ; the lakes which supply the 

 city of Halifax with water, Grand Lake and Dartmouth Lakes in 

 Halifax Co. ; and Kempt Lake, in King's Co. 



Lists of the species of Diatomaceaj and Spongidee detected in the 

 several deposits wei'e given in the paper, which was accompanied by 

 microscopical slides and specimens. The author has not yet con- 

 cluded his researches. 



5. — Plan for the Subject Bibliography of North American 



Geology. 

 By G. K. Gilbert. 

 rpHE United States Geological Survey is engaged on a Biblio- 

 JL graphy of North American Geology. The work when com- 

 pleted will give the title of each paper, with the title-page of the 

 containing book, and the number of plates, the whole being arranged 

 alphabetically by authors. 



There is in contemplation also the simultaneous preparation of a 

 number of more restricted bibliographies, each covering a division of 

 geological literature. The plan includes abbreviated titles of papers, 

 with reference to the pages on which the special subjects are treated, 

 the entries in each bibliography being arranged alphabetically by 

 authors. 



The selection of topics for treatment in this manner involves the 

 classification of geologic science, and Mr. Gilbert submitted a tenta- 

 tive classification, requesting the criticisms of geologists. 



