24 Transactions of the Soeiety. 



stone and " rools," carrying the preparation with it. The slide is 

 now washed with a camel's-hair brush and by means of a jet of 

 water. It is then stood up to drain and left to dry. When the 

 drying is complete (an important matter) take a soft camel's- 

 hair brush and wash the surface of the specimen with equal parts 

 of turpentine and benzol or chloroform, until the network begins 

 to look raised; then drain but do not dry it. Drop on balsam 

 dissolved in benzol or chloroform, and finish the slide in the usual 

 way. 



It is sometimes useful to employ the air-pump, but it should 

 be done slowly and no attempt made to produce a high vacuum. 

 The specimens improve very much at the end of a week or a 

 fortnight. 



The above process may appear long and tedious, but after a 

 short apprenticeship the different processes become easy, and by 

 preparing a number of sections simultaneously no large amount of 

 time is consumed. The study of vesicular rocks is the key to the 

 principal phenomena of volcanic eruptions, and by its means we 

 can read the different phases in the history of any volcano we 

 choose. In addition, the specimens so prepared form very beautiful 

 slides (especially in the case of a moderately crystalline pumice). 

 It need hardly be said that it has one great recommendation, and 

 that is that no expensive apparatus is required, whilst the method 

 may be extended to other structures. In this way Dr. Yosmaer, 

 of the Naples Zoological Station, and myself have succeeded in 

 applying the method to siliceous sponges, and we are now en- 

 deavouring to modify the method so as to prepare sections of them 

 with the sarcode intact. 



