C. G. Gmelin on Clinkstone ur F/ionolite. 71 



magnesia, the latter a considerable proportion. Magnesia and 

 oxide of iron in general shew a great tendency to enter into 

 combination with each other. 



7. It is well known that chnkstone mountains ai-e favourable 

 to the growth of plants, particularly for the growth of vines. It 

 appears from the analysis of the weathered and fresh clinkstone 

 of Abstrodc, 1. That, during the process of weathering, nearly 

 the greatest part (about three-fourths) of the mesotypic consti- 

 tuent part of the clinkstone, which can be decomposed by acids, is 

 removed : 2. That the removal of these constituent parts does not 

 take place in an uniform manner, but that certain constituents 

 only are principally removed by the influence of the weather. 

 Thus we observe, that nearly the whole of the alkali, and the 

 greater part of the siUca and alumina, have disappeared, while 

 the quantity of oxide of iron and oxide of manganese has much 

 increased. The tendency of clinkstone to part with its meso- 

 typic constituent part, through weathering, by which a large 

 quantity of alkah is carried into the soil, may explain the luxu- 

 riance of the vegetation on the sides of chnkstone hills, whose 

 highest summits only are bald. 



8. May not volcanic rocks, as basalt and chnkstone, answer 

 well for building under water, and, therefore, take the place of 

 puzzolana and trass ? May not the hydraulic character these 

 rocks possess, def)end on the loose state in which a part of the 

 silica exists ? At least, all these rocks, however different their 

 composition may be, have this property in common. It is 

 worthy, therefore, of inquiry, whether the quality of hardening 

 under water with lime, increases with the quantity of matter 

 which gelatinises.^ Whether the weathered mass, deprived of 

 its gelatinising mass, loses this property .'' Whether the pure ge- 

 latinary mass itself, as the natrolite, for example, possesses this 

 property, and in a marked degree .'' The determination of these 

 questions are important for the theory of hydraulic mortar. 



