INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 325 



In studying the grains of sand, Dr. Sorby by sifting rejects those 

 more than ^l of an inch in diameter or below y^^j, so that an 

 average of y J^ is obtained. He was astonished in working in this 

 way to find that what seemed all similar to the naked eye contained 

 really five well-marked types — (1) the angular ; (2) the well-worn 

 rounded ; (3) the mechanically broken ; (4) the chemically corroded ; 

 (5} the perfect crystal. It is important to distinguish between the 

 age of the grains and the age of the deposit. A very old bed may 

 contain grains but little modified, while a younger bed may have very 

 old grains — that is, grains that have passed through many vicissitudes, 

 and have belonged successively to many different formations. Several 

 practical tests of the value of the method were mentioned with 

 reference to the study of the age and conditions of the beds as 

 compared with the results deduced from other methods — for exami^le, 

 the sharp angular sand-grains of the boulder clay well accord with 

 the theory of its glacial origin. 



Cutting Rock-sections. — At the December meeting of the San 

 Francisco Microsc()j)ical Society, a paper by Mr. M. Atwood was read, in 

 which he described a plan of cutting rock-sections for the Microscope 

 at little cost and labour. He uses a few emery stones, or blocks, of 

 different degrees of fineness — say, from one and a half to two inches 

 square, and eight or nine inches long. The chips to be cut should be 

 first made as thin as possible ; the plan recommended by Mr. Rutley, 

 to use a cold-chisel, the end let into a block of wood, and then by 

 holding the specimen on the edge of the chisel and striking it a sharp 

 blow with a light hammer, will generally give a satisfactory chip. The 

 chip must then be rubbed on the emery blocks, with water, till a good, 

 even surface is obtained on one side of it, commencing with the 

 coarse emery blocks first ; then, with Canada balsam, fasten the 

 smooth surface of the chip to a common glass slide, which is done by 

 heating the slide over a spirit lamp and then applying a small 

 quantity of the balsam. As soon as the balsam liquefies, press the 

 smooth surface of the chip into it, and allow it to cool. The balsam 

 is better dried, so that it can be used like a stick of sealing-wax. As 

 soon as the slide and chip are cold, the outer, or rough surface of the 

 chip attached to the slide, can be rubbed on the emery blocks until it 

 is nearly thin enough for mounting. To finish, use the fine, smaller 

 blocks, as you would a file. The section can bo held up to the light 

 and examined during the operation. Mount and cover the section 

 with thin glass, in the usual way. 



Amongst the specimens shown were two, which were cut in 

 London, by a professional, with expensive api)aratus. Two others 

 were from the same rock, but cut by the author, with the emery 

 blocks, in the way described, and, if tlie mounting material was of as 

 good quality, would have been equal to the former in every respect. 



New Preservative Liquid.* — Under the title "The Wickers- 

 lieimer metliod of preserving " is described a i)rocess whicli claims to 

 preserve human and animal bodices witli their proper form, colour, 



♦ ' Zool. Aiizci^'or,* li. (1S7U) p. GUI). 



