1877-] 
Scientific Notes . 
567 
The Rev. A. Renard, of Louvain, has contributed to the “ Transactions of 
the Royal Microscopical Society ” a valuable treatise on the “ Composition 
and Microscopical Structure of the Belgian Whetstones.” The rocks ex- 
amined were those in the neighbourhood of Viel-Salm, in the province of 
Liege, Belgium. The stones are in shape parallelopipeds, composed of a 
stratum more or less deeply coloured yellow, and of a stratum coloured blue- 
violet, and constitute the well-known “razor-hone.” The hones of Viel-Salm 
are found amongst the rocks which Dumont calls Salmien, but seem to re- 
semble very much the English Cambrian, and to be the equivalent of the 
schist of Tremadoc. The blue and yellow layers, although apparently sepa- 
rated by a distinct straight line, are so intimately united that the workman 
has nothing else to do than to square the fragments. The mirrute structure 
of the rock is very remarkable. A fibrous pliation oblique to the stratification 
is prolonged from the slate into the whetstone ; and if the slate be broken the 
lamina comes off, passing across the whetstone and the fissure is prolonged 
with a regularity and constancy of angle which shows evidently that the two 
rocks have a common cleavage. The author is of opinion that the whetstones 
are contemporary layers with the incasing slates, and have been subjected to 
the same mechanical adtions as all of the phylladic rocks of this group. The 
mineral composition and the microscopical and optical structure have been 
carefully studied by the Abbe Renard. The matter is highly interesting, but 
does not admit of a useful abstract being made, and occupies too much space 
to quote in full. The paper affords another instance of the great value of the 
microscope, and especially the service rendered by the polariscope to the 
investigation of substances hitherto regarded as almost structureless. 
Specimens of fossil Polyzoa are frequently obtained in which the least inte- 
resting side is the one exposed to view. Mr. John Young, of the Hunterian 
Museum University, of Glasgow, has communicated to “ Science Gossip ” 
(July, 1877, p. 158) a process by which the specimens may be detached from 
the original matrix, and mounted so as to show the side hitherto out of view. 
The specimens suitable for the process are those imbedded in shales that yield 
readily to the disintegrating influence of the weather. Very little can be done 
with specimens imbedded in hard calcareous shells or limestone. After se- 
lecting the specimens of Polyzoa it is best to let them be well dried at a fire 
or in the sun for a few days, to secure the adhesion of the asphalte used in 
mounting. When a specimen is to be operated upon let it be heated before 
the fire, and a layer of asphalte melted over it with a piece of iron heated 
nearly to redness. The asphalte used is the common sort, free from sand, 
employed in street paving. While hot, press a piece of tough brown paper 
down over the surface evenly with the fingers. The paper strengthens the 
asphalte very much, and afterwards, when the specimen is mounted, the paper 
adheres to the tablet on which it is fastened better than when asphalte is used 
alone. When large fronds of Polyzoa have to be lifted from the shale, then a 
second layer of asphalte and brown paper is employed : this forms a firm 
thin cake, which in large specimens is less likely to break across. The next 
operation, after fixing the asphalte to the fronds of the Polyzoa, is to place 
the specimens in water, and let them lie until the shale softens. In some 
cases the Polyzoa parts from the shale in a few minutes ; in others an hour or 
two, or even a day, may be required. The process may be hastened by placing 
the specimens in a saucer filled with water, and, as the shale is softened, keep 
picking it away with a thin sharp knife until the fronds of Polyzoa appear ; 
then with a worn nail or tooth-brush mash the surface of the specimens until 
they are quite clean and the cell-pores well exposed. If the fronds have been 
well fixed to the asphalte, the greatest freedom may be used in mashing the 
specimens without fear of their removal by the brush. For cleaning small 
specimens of Polyzoa intended for microscopical examination, the following 
method may be employed : — After having picked the specimens out from 
amongst the weathered limestone shales, where they often have a thin layer 
of clay adhering to them, take a glass slide and cover it with a layer of thin 
gum; then with the forceps lift all the fragments of Polyzoa to be cleaned, 
and place them on the slide with the poriferous face uppermost, afterwards 
