ABOUT MANCHESTER. 153 



It has some peculiar properties, as that of form- 

 ing a good cement under water. Geologists call 

 it Magnesian Limestone^ because it is found in 

 a certain position, relatively to other strata. In 

 appearance, it agrees pretty nearly with one of 

 24 specimens of mountain limestone (so called) 

 which I have from a district of 20 miles circuit, 

 in Cumberland ; but it has very little resemblance 

 to the true magnesian limestone from Yorkshire. 

 When analysed, it appears to be pure carbonate 

 of lime, united or mixed with two per cent, of 

 clay, and a considerable trace of iron, perhaps 

 half of a grain per cent. It is probably owing 

 to the two last ingredients, that its peculiar qua- 

 lities are to be ascribed. It contains no more 

 magnesia than chalk and mountain limestone in 

 general do, which is a slight trace. Whereas, 

 the true magnesian limestone, found in some parts 

 of Yorkshire, and, perhaps, in other counties, 

 contains the two elements of lime and magnesia, 

 united, nearly or accurately, in atomic proportion, 

 or the hme to the magnesia as 24 : 17. This is 

 the case with the two specimens now presented 

 to the society. Their specific gravity, too, is ge- 

 nerally below that of mountain limestone. 



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