212 



SCIEXCE-GOSSIP. 



powder, see that it has now a lustrous aspec:, a- d :he 

 crystals of which it is composed are much better 

 observed than before. Now take a glass slip and. 

 ha\-ing warmed it, put on some Canada balsam 

 and heat all over a spirit-lamp, spreading out the 

 balsam carefully so that it shall occupy a space on 

 the sUp fully equal to the area of the piece of rock. 

 Do not heat the balsam to too high a point, or too 

 long. ^^Tien it has cooled somewhat, place the flat 

 side of the specimen on it and move it about so as to 

 displace all air bubbles between it and the slip . "V^Tien 

 all is quite cold, proceed to grind the rough upper 

 side of the section in pretty much the same way as 

 has been described. Rasp, coarse and fine file, 

 emery powder coarse and fine, putty powder very 

 fine, such is the order of procedure. As the opera- 

 tion continues, by holding the slide up to the hght, 

 some of the altered felspar crystals will first get 

 transparent, it being nearly possible to see through 

 them ; but do not feel too elated, as the work is not 

 quite finished. In point of fact, the most delicate 

 and difficult part of the whole process is to decide 

 definitely when it is thin enough or otherwise. 

 The best finish is a rub on a fine hone moistened 

 with paraffin. A good general rule is, that the 

 section is thin enough when, on moistening it Asdth 

 water, ord in ary printed letterpress can be dis- 

 tinguished through it. This tna^im holds good in 

 aU cases, except where the presence of much oxide 

 of iron or other rn^-incibly opaque mineral occupies 

 a very large area of the section. Hovsever, we will 

 suppose that the operation on the whole has 

 been neatly and completely done, and that %ve 

 are bursting with impatience to see what there is 

 under the microscope. The finish and mounting 

 must be carefully manipulated. Take a large 

 camel-hair brush with some clean water, and 

 persistently clean away firom the slide every 

 particle of dirt or dust ; then dry it and do the 

 same again, using benzene or xylol this time, so that 

 everything may be clear of extraneous particles. 

 Be extremely careful not to put turpentine or any 

 other essential oil on the section, and do not mount 

 it in balsam. The best mounting medium for rocks 

 that I know is a solution of gum-dammar in xylol. 



Supposing that a satisfactory mount has been 

 accomplished, we can now, with microscopic help, 

 endeavotu: to observe the structure and constituents 

 of the rock. A wide-angled half-inch objective is 

 very serviceable for this purpose, and let us there- 

 fore use it to view a section of a moderately fine 

 specimen of a rock which, according to a Fellow of 

 the Geological Society, " affords abundant evidence 

 in its structure and composition that it was derived 

 from a similar source and in a similar manner to 

 the beds of recently-formed volcanic ejectamenta 

 which may be seen surrounding the cone of an 

 active volcano." The difference, however, in the 

 case before us is, that the rock, as old as the 



Silurian age, has been considerably metamorphosed 

 bv time and en\"ironment, bv heat, pressure and 

 aqueous agencies. Hence, instead of seeing fresh, 

 clear and well-formed crj-stals of felspar, augite, 

 etc., we see now onlv turbid ones deformed and 

 broken, and internally quite changed into other and 

 different minerals. Two principal objects are 

 observed in the section under re\dew. First, there 

 are a large number of whitish turbid forms of an 

 approximately crystal shape : these were originally 

 clear felspar prisms, but are now deformed and 

 broken, with their edges more or less ill-defined or 

 irregularly rounded, their relative hardness and 

 infusibility, however, preser^dng them from total 

 destruction, notwithstanding that metamorphic 

 agencies have transmuted them internally into 

 caldte and mica flakes, chlorite and quartz. Along 

 vdth these there are a much smaller number of 

 clear chlorite crystals vrhich were originally augite, 

 probably black and opaque. Secondly, these larger 

 constituents are embedded in a powdery "base" 

 which is much more injured and disordered than they, 

 it being very cloudy and composed of a semi-opaque 

 heterogeneous powder interspersed with patches of 

 green chlorite, dark brown oxides of iron, etc. 

 This base represents the fine dust which resulted 

 from the destruction by volcanic explosion of the 

 softer minerals, such as augite, enstatite, garnet, 

 magnetite, glassy residuum, etc., of which the 

 original lava was composed ; and " we may look 

 upon it that the original andesitic and other 

 volcanic dust of the rock has decomposed in such 

 manner that the augite, etc., gave rise to chlorite 

 with garnet, while the felspathic part of the 

 mixture was largely altered to mica." (Hutchins.) 

 Patterdale, mar Penrith. 



B.^TS .-iXD Music. — On more than one occasion 

 I nave drawn attention in these pages to the 

 influence of man's civilization on wild animals. 

 For the past month I have noticed that a common 

 species of the small bat, probably the pipistelle, 

 which frequents the towns in Southern France, 

 congregates in the evenings about those cafes 

 where it is the custom to have outdoor music. 

 This does not seem to apply to any particular 

 town, as they are to be seen flitting about in the 

 crowded streets amongst all the traffic in Marseilles, 

 Cannes, Nice arid Monte Carlo. So tame are some 

 individuals that they hawk about for flies under 

 the awning which covers the chairs placed on the 

 footpaths. It may be said they come for the flies 

 attracted by the electric lights, but the bats are far 

 more numerous near those cafes where there is 

 music than around the ordinary arc-hghts in streets 

 or before shops. The inference appears to be that 

 they find pleasure in the presence of music. — John T. 

 Carrington, Beaulieu, Alpes Marithms ; Nov. 2xst, 1896. 



