COLLECTION, EXAMINATION, ETC. 301 



Hakes still remain unbroken, the material must again 

 1)6 dried and Avashed. 



In the case of shales or indurated muds, such as 

 Kimeridge shale, or the shaly material found as 

 partings between the joints of the Carboniferous lime- 

 stone, a slightly different treatment may be required, 

 and the material must be broken up mechanically 

 into smaller pieces before washing. Should the work 

 be prosecuted in winter, we may be able to take 

 advantage of a severe frost by exposing the material, 

 just covered with water, to the action of frost, which 

 materially aids its disintegration. But by these means 

 even, it will be found impossible to reduce the whole 

 of the material by washing, and in this case we must 

 have further recourse to sifting after the material is 

 dried, in order to select that portion which will yield 

 the best results when it is sorted. Hard marls may 

 often be broken up by boiling the fragments in a flask 

 with sulphate of soda. 



Calcareous sandy rocks, such as the Crag deposits, 

 can only be sifted, in the majority of cases, on account 

 of the friable character of their Foraminifera. 



Soft limestones, such as Chalk, can generally be 

 readily broken dow^n by first selecting pieces, not larger 

 than hazel nuts, of the softest material from the 

 particular stratum one wishes to examine, tying them 

 in a strong coarse linen bag, and thoroughly soaking 

 in water. The bag can then be pressed and kneaded, 

 so as to crush the lumps of chalk, and the milky 

 water strained off. This process should be followed 

 so long as the water in which it is steeped is made 



