NOTES AND MEMORANDA. 235 



grey colour, or perfectly wtite, and extremely light and pulverulent 

 in texture. On the Western coast, through California, Oregon, 

 Washington territory and Nevada, there exist vast tracts covered by 

 fresh-water deposits of Diatomacete, which are hard and stony. They 

 have become so by the action of superimposed lava and basalt. Now, 

 it is a remarkable fact that there have come to light two deposits 

 from the Atlantic coast, possessing very much the same physical cha- 

 racters as these Western strata ; that is to say, they are hard and 

 stony, and almost white in colour. One of these was presented at a 

 meeting of the Lyceum some time since, by Dr. L. W. Feuchtwanger, but 

 unfortunately its exact locality has not been ascertained. The other is 

 from New Hampshii-e, and all of the facts connected with its manner 

 of occurrence, doubtless will be brought to light, as Prof. Edwards is 

 at present engaged on the microscopical department of the geological 

 survey of that state, now being prosecuted under the superintendence 

 of Prof. C. H. Hitchcock. A very extonsive lacustrine sedimentary'- 

 deposit of the pulverulent kind, and almost white in tint, has been 

 discovered on the shores of Lake Umbagog, in New Hampshire, and 

 there were indications that it extends beneath the waters of the lake, 

 perhaps over the whole bottom. These deposits are of interest, geolo- 

 gically and microscopically, but at the same time commercially, as they 

 have been used to some extent, not only as polishing powders, but as 

 a source of very finely divided silica, of which the skeletons of the 

 Diatomaceae they contain are made up, for the manufacture of soluble 

 silicates, or " soluble glass " as it has been called, which is now a 

 considerable article of trade. Although existing for the most part in 

 strata of no very great thickness, or usually covering no more than a 

 few acres of ground, yet, as the number of localities from which they 

 have already been procured in the Atlantic states is over a hundred, 

 the supply for commercial purposes is amply sufficient, without having 

 to draw upon the vast tracts covered by the lake deposits of the 

 Pacific coast, or the marine strata of California and Virginia. In a 

 forthcoming volume of the Report on the Geology of California, the 

 whole subject of these deposits, their mode of formation, with descrip- 

 tions and figures of the organisms found in them, will be published, 

 when will be cleared up several points of interest with regard to 

 them. 



' The History of Zoology,' by Victor Carus, is already in great 

 part printed. 



Rocks and Dredgings from the Gulf Stream. — These have re- 

 cently been chemically examined by Mr. S. P. Sharjjles. From a 

 microscopic examination of some of the bones, he says that there was 

 little but fibrous structure remaining. They were of a Manatee. 



Monochromatic Light. — A correspondent, who does not give his 

 name, and whose letter we therefore cannot insert, inquires what is 

 meant by this term. We really did not think there was any difficulty 

 about the matter. It simply means light of a single colour : thus 

 red, blue, or yellow light, wotdd be monochi'omatic. We think Col. 

 Woodward explains the matter sufficiently. At page 153 he says, 



