10 
Arthur Aikin, Esq. on a series of 
The earthy matter adherent to some of the specimens, and which 
I consider as haying formed part of the lava, No. 11, is deeply 
coloured by oxide of iron, has a completely earthy appearance, and is 
in general but little coherent. The only distinct minerals which I 
have observed to be contained in it are, scales of yellowish and 
silvery white mica, usually very minute, and pieces (which appear 
to be fragments) of finely granular carbonate of lime, effervescing 
strongly with acids. 
The specimens of glass in this collection are particularly interest- 
ing, as shewing a variety of changes which this substance is capable 
of undergoing, by the continued action of a moderate degree of 
heat. 
No. 1 is a fragment of a looking-glass, seeming at first sight to 
have undergone no alteration, except that the metallic lustre of the 
silvering is gone, and the upper surface of the glass appears as if it 
were dirty : this dirt, however, is not to be removed by washing 
with water, and on inspection with a lens appears to be the com- 
mencement of a decomposition or change of structure, for in the 
dull parts are seen many small circular portions that still retain their 
lustre, and some little cavities appear where the substance of the glass 
has been more rapidly acted on than elsewhere* 
No. 2 are specimens of glass exhibiting the next change of 
structure : some of these are merely become dull and almost opake 
superficially, the interior being unaltered ; in others may be seen the 
commencement of a fibrous structure, penetrating from each surface 
to the depth of about one-eighth of an inch into the interior of the 
* • 
mass* 
Nos. 3 and 4 are masses composed of flat pieces of glass, which 
having been softened by exposure to a heat almost equal to their 
fusion, have sunk down upon each other, without, however. 
