240 



^remarkably close and compact nature was obtained from vei*tical 

 fissures in the Great Oolite, and is probably derived from the 

 Boulder Clay ; it is remarkable for its high percentage of oxide 

 of iron, and almost entii'e fi-eedom from lime. It was found to 

 consist of silica 51 parts, oxide of iron and alumina 32 with a 

 trace of oxide of manganese ; this clay the Professor stated was 

 admirably adapted for the manufacture of pottery. 'No. 4. — 

 From the Forest Marble showed the blue centre, &e., character- 

 istic of the limestones of that formation. This blue centre was 

 shewn to contain a much larger proportion of iron and sulphtir 

 than the surrounding lighter portion. The Professor shewed 

 that the lighter coloured portion of stone surrounding the blue 

 centre never penetrates to a greater depth than from one to two 

 inches, the difference of colour being due to jjeroxidation, pro- 

 duced by the percolation and absorption of water. 



Professor Chukch exhibited experiments connected with his 

 researches into the colouring matter in the wings of certain 

 African Birds, the Touracos and Plantain-eaters. The wing 

 feathers of these birds, of a splendid magenta crimson, are found 

 to part with their colour by maceration in water, and when 

 this action is intensified by the addition of an alkali, and the 

 result is precipitated by an acid, a solid crimson floccose deposit 

 is the result, which upon analysis proves to be indebted for its 

 colour to the presence of copper. 



The whole question of the process whereby nature colours 

 with unerring exactitude the feathers of birds, is among those 

 marvels of life-action which human knowledge may never 

 explain, because it is carried on in a laboratory so secret and by 

 processes so fine and imperceptible as to escaj)e detection by 

 the keenest observation and the most delicate tests. But in the 

 instance under review the marvel is intensified by the fact that 

 the colouring mattei' — itself the product of a rare metallic 

 agent — is applied only to a certain and exactly defined portion 

 of the plumage, while another portion in immediate contact, on 

 the same feather, shews no trace whatever of the peculiar 

 mineral. 



After dinner Mr. Gr. F. Platne drew the attention of the 



