PROCEEDINGS OF GEOLOGICAL SOCIETIES. 



437 



be operated upon with a thin coating, not exceeding the sixteenth of 

 an inch. Haying obtained a smooth even surface of the gutta-percha, 

 warm the specimen by dipping it into warm water, or otherwise, and cover 

 it with the preparation. It is advisable sometimes to wet or oil the 

 specimen previously to putting on the gut'ta-percha, to prevent it ad- 

 hering. It must now be well pressed on the specimen, in order that it 

 may delineate the more delicate structure, and this manipulation must bo 

 continued until it becomes hard ; then remove it from the specimen, or, 

 if necessary, cut it with an oiled knife. Previous to cutting, marks 

 should be made, to ensure the mould being correctly joined in taking 

 the plaster-cast. It is desirable to make a small hole in one of tho 

 pieces, to allow the plaster to be poured in. 



3. Maldwj the ^;?«.st^r-m.s^ .-—Sprinkle the plaster into a basin con- 

 taining water enough to fill the required mould. Mix it well until it 

 forms a thick paste ; it is then fit for use. 



Take the pieces of the gutta-percha mould, and join them by means 

 of India-rubber bands, exactly according to tho marks previously made. 

 A small quantity of plaster is then poured into the opening, and the 

 mould is turned round several times. This must be done quickly, as the 

 plaster dries very rapidlj'. More plaster is added until the mould is full. 

 It is then left for a few minutes to set. The mould is then taken oil', 

 and well cleaned, to be ready for another casting. The tools should bo 

 put into water immediatel}^ after using them, to prevent the trouble 

 which otherwise arises from the hardening of the plaster. 



In taking a plaster-cast from a large open gutta-percha mould, after 

 carefully oiling the surface of the latter, the moist plaster should be first 

 poured on in a fluid state, and carefully and quickly worked into all tho 

 irregularities of the surface by means of a stiff brush; a shortened 



painter's tool" is best for the purpose ; and the plaster subsequently 

 added should be cautiously and continuously jogged, holding the mould 

 between the hands, and knocking its base on the table with steady, 

 slight successive blows, so as to ensure the bubbles of air leaving the 

 mould, and rising to the top of the plaster, as long as it is fluid. 



It is often advisable to place the ends of a piece of folded string in 

 the soft plaster whilst making the cast, to supply means of pulling at 

 the cast to release it from the mould. 



London, August 23rd, 1858. 



liEPOETS OF THE PROCEEDINGS OF GEOLOGICAL 

 SOCIETIES. 



East Kent Natural History Society. — Tlie East Kent Natural History 

 Society held their annual meeting on the 28th of August, and selected Dover as 

 their head-quarters upon tho occasion. The Association has been in obscure 

 existence some years, but appears to have been lately revived with great vigour, 

 and -we hope will long continiie to labour earnestly and well in a district in which 

 much as has been done, so much yet remains to do. 



The arrangements of the day comprised the double attraction of an excursion in 

 the morning and a dinner in the evening ; the scene of the first portion of this 

 programme being the coast lying between Folkestone and Dover. The gathering- 

 was further favoured by splendid weather, and by every other external circuia^ 

 s1;aoce which could contribute to ensure its complete sugcess. 



