

136 THE NORTHERN MICROSCOPIST. 

been established it would be a questionable thing to make other 
sections of these rocks. But there is a vast amount to be learnt, 
and I would not hinder anyone from attacking such questions. 
Then I found that you might take a somewhat similar method 
in preparing sections of very soft material indeed. The chalk on 
the Yorkshire coast is so very hard, and almost a limestone, that 
there is no difficulty in preparing thin sections; but the chalk of 
the South of England is exceedingly soft and friable, and you can 
brush it into fine material and study the minute foraminifera and 
coccoliths that constitute such a large proportion of it. But it was. 
important to study the natural condition of the chalk,—not to 
wash it and study the débris, but to ascertain its condition when 
all the particles were zz sé#?, and I found no difficulty in doing 
that. Irubbed down a portion of the chalk into a convenient 
size, and then hardened it with balsam by soaking it in turpentine 
so as to get all the particles well wetted, and then putting on it a 
lot of Canada balsam and keeping it hot for some time. The 
balsam thus sinks into the chalk, and ultimately all the cavities are 
filled with hard balsam, and you can deal with it as though you 
were dealing with a rock. You rub it down and mount it on 
glass in the usual way, but you must take care that you have got 
the balsam very hard, and must take care not to make it very hot, 
because if you should it would all break to pieces. You can in this 
manner get sections of very soft chalk, and even of clay, if you 
desired to study the way in which the particles were associated in 
the material. 
In the case of chalk, you may compare the soft chalks of the 
South of England with the hard ones of the Yorkshire coast. 
When you study the structure of the soft chalks you find that the 
cells of the foraminifera are empty, unless they may be filled with 
the soft chalk. Perhaps you might see a little crystal of calcite 
here and there, but as a rule the foraminifera and minute shells 
are wholly empty. In the case of the chalk of the Yorkshire coast,. 
however, you find all the cavities filled with calcite. The Southern 
chalks are as they were deposited ; there has been no introduction 
of soluble carbonate of lime to crystalise and fill the pores. But 
in the Yorkshire chalk carbonate of lime has been infiltrated and 
hardened the whole. 
I remember making some experiments by ascertaining the 
increase in weight when thoroughly soaked in water, and calculating 
from the difference in the specific gravity the volume of water 
absorbed ; and it was interesting to see what a large amount of 
empty space there was in the chalk of the South of England, but 
very little in the Yorkshire chalk—the whole having been consoli- 
dated by the introduction of carbonate of lime. 
In preparing sections of mica-schist, notwithstanding all the 


