A SUMMER RAMBLE AMONG THE HEBRIDES. 195 



most always a definite proportion to the amount of animal 

 matter round which it had formed. I was a good deal struck, 

 a few weeks ago, in glancing over a series of experiments 

 conducted for a different purpose by a lady of singular in- 

 genuity, Mrs Marshall, the inventor and patentee of the 

 beautiful marble-looking plaster, Intonacco, to find what 

 seemed a similar principle illustrated in the compositions of 

 her various cements. These are all formed of a basis of lime, 

 mixed in certain proportions with organic matter. The reader 

 must be familiar with cements of this kind long known among 

 the people, and much used in the repairing of broken pottery, 

 such as a cement compounded of quicklime made of oyster- 

 shells, mixed up with a glue made of skim-milk cheese, and 

 another cement made also of quicklime mixed up with the 

 whites of eggs. In Mrs Marshall's cements, the organic 

 matter is variously compounded of both animal and vegetable 

 substances, while the earth generally employed is sulphate 

 of lime ; and the result is a close-grained marble-like com- 

 position, considerably harder than the sulphate in its origi- 

 nal crystalline state. She had deposited, in one set of her 

 experiments, the calcareous earth, mixed up with sand, clay, 

 and other extraneous matters, on some of the commoner mol- 

 luscs of our shores ; and universally found that the mass, in- 

 coherent everywhere else, had acquired solidity wherever it 

 had been permeated by the animal matter of the molluscs. 

 Each animal, in proportion to its size, is found to retain, as 

 in the fossil iferous spindles of the Old Red Sandstone, its 

 coherent nodule around it. One point in the natural phe- 

 nomenon, however, still remains unillustrated by the expe- 

 riments of Mrs Marshall We see in them the animal mat- 

 ter giving solidity to the lime in immediate contact with it ; 

 but we do not see it possessing any such afiinity for it as to 

 form, in an argillaceous compound, like that of the ichthyo- 

 lite beds, a centre of attraction powerful enough to draw to- 



