66 SUPPLEMENT TO THE 



I am the more anxious to republish, as it may induce some other geologists, favorably 

 placed, to undertake similar washing operations so beneficial to science. 



" The occurrence of cleanly-washed fossils in the debris remaining from many of 

 the clays and shales suggested to me that the potter's process of laevigation might be 

 conveniently employed by the geologist for the collection of fossils (especially of the 

 smaller species), from the soft shales, in which hand-picking is at best a most laborious 

 process. 



" The potter's object in levigating clay is to get rid of the coarser matter. The 

 fossil-collector pursues, as it were, the process in reverse, by getting rid of all the clay 

 and fine matter, and obtaining in a condensed form the coarse debris, including the 

 organic remains. 



" A potter's 'blunging' or clay-laevigating machine, though it greatly facilitates the 

 process, and enables large quantities of material to be quickly laevigated, is not essential, 

 as an experienced worker can in a day easily laevigate several hundredweights of clay or 

 soft shale, with the aid only of a tub and a stout wooden stirrer. 



" The operator should provide himself with a set of sieves of the following mesh : — 1, 

 2, 4, 6, 10, and 12 wires to the inch. 



" Having digested in water, say, half a ton of material, the ' slip ' or liquid clay is 

 poured off through the No. 12 or finest sieve, which catches any very small fossils ; and 

 the remaining debris, which might weigh about a hundredweight, should be repeatedly 

 washed with fresh water, by which all fine matter will be removed, and the material 

 remaining will in most cases resemble clean coarse gravel, with which the operator will 

 have further to deal. As this will-ultimately be the subject of the laborious process of 

 hand-picking,' it is desirable to reduce its bulk as much as possible. The whole is 

 first passed through the sieve of one-inch mesh, which catches all the stones, lumps of 

 undigested shale, and the larger fossils, which are easily picked out. The mass is thus 

 reduced to half or perhaps two-thirds of its weight, and is then dried. It greatly facilitates 

 further operations to sort this into separate sizes by passing the dried material succes- 

 sively through the sieves of \ inch, g^th of an inch, and ^oth of an inch mesh. The fine 

 matter passed through the -^jth of an inch mesh seldom contains fossils, and may be 

 thrown away. 



" Now comes the final process of hand-picking from the three sorted lots of debris. 

 These are spread out thinly on a slab of slate or a smooth board, and women, at a wage 

 of Is. Gd. a day, quickly perform the operation, and readily learn, not only to pick out 

 the fossils from the gravelly debris, but also to roughly sort the species. 



" As an instance of the good results of this process, I would mention that from 

 one cartload of the Buildwas Beds of Wenlock Shale no less that 4300 specimens of one 

 species, Ort/iis biloba, were obtained, besides a much greater bulk of other Brachiopods, 



1881. Since then I have made several changes and additions to the Table of Species, which I prepared 

 and published at that period. 



