308 NATURAL SCIENCE. November. 



be so thoroughly cleared by the brush that it should successfully 

 stand the scrutiny of a strong hand lens. Indeed, no specimen can 

 be considered clean until it will pass this ordeal. 



The bristle brush can be used for working fossils in a damp 

 state, and if the Grey Chalk and Chalk-marl specimens are worked 

 in a moist condition (not soaking wet) beautiful results may be 

 obtained, even in such awkward cases as clearing the long spines of 

 Ostrea cavinata. The Grey Chalk Salenias and Pseudodiademas are 

 often quite impossible to clean in a dry state, and if care be taken to 

 avoid using too much water, the urchins may be freely handled. 



Anyone who has attempted to clean echinoderms of the nodular 

 chalk of Dover, of the Melbourn Rock, or of the Chalk-marl, will have 

 been reduced to despair by the way in which portions of the matrix 

 decline to be removed. A very good plan is to reserve the stumps ot 

 the half-worn bristle brushes for these obdurate specimens, or in the 

 case of the Holasters and Hemiasters of the Grey Chalk and Chalk- 

 marl, to use the fine brass brush. This brush is of the same size as 

 No. i. bristle brush, and is made of crinkled brass wire, as fine as silk, 

 and it does no harm. Some patches, however, are so grown into the 

 surface of the shell that nothing will remove them, and the dry brush 

 will even polish them. 



If one may judge from the grimy state of many Chalk fossils in 

 public museums, not one of the least useful functions of the engine 

 will be found in the case of the large badger-hair brush, which takes 

 a thin film of matrix off flat surfaces without cutting into the specimen. 

 Thus a fresh surface can in a few seconds be given to a block, without 

 laboriously paring away the chalk with a knife, with the certainty of 

 reducing the specimen to the vanishing point in course of time. 



While on the subject of touching up old specimens, it may be 

 well to mention that all hard fossils can be safely cleaned by dabbing 

 them with cotton wool soaked in methylated ether. Many specimens 

 would split if water were brought in contact with them, but the ether 

 evaporates so rapidly that no harm is done. 



The variety of instruments which can be fitted into the hand- 

 piece of the engine varies only with the ingenuity of the worker, and 

 special burs can be used for smoothing down the surface of Chalk- 

 marl blocks, or drills can be made for piercing them. 



As a lubricant for the engine nothing excels a white odourless 

 hydrocarbon oil, which goes under the name of oleum deelinae, or 

 paroleine. Moreover, one can keep the steel burs, brushes, and drills 

 in the same excellent fluid ; and if a wide-mouthed bottle is filled 

 with river-sand soaked in the oil, the scalpels can be stuck into the 

 sand, and left with impunity even in a damp workshop. 



The choice of an engine is a matter of no small moment, both 

 from the point of view of cost and efficiency. What is wanted is a 

 short, second-hand instrument, which is easy to work sitting down. 

 Never mind if the engine is not a thing of beauty, so long as it goes 



