164 ROCK STRATA ABOUT MANCHESTER. 



6. Tinker S' Brow Limestone, 

 2.65 Specific Gravity. 



There is some limestone found at Tinker*s 

 brow, which may be supposed an edge of the 

 Ardwick stratum. The analysis of this specimen 

 shews it to be a compound or mixture of carbo- 

 nate of lime and clay. The two earths of lime 

 and clay, are nearly in atomic proportions ; but 

 this may be merely accidental. The lime only 

 is combined with carbonic acid. It contains 

 rather more iron than the Ardwick stone. Ex- 

 clusive of the iron, I found the compound to be 



nearly 36 clay, 



36 Ume, 

 28 carbonic acid. 



, 100 



7. Yellow Clay Stratum. 



A portion of a stratum of yellow clay, from 

 Broughton-grove, was treated with dilute pure 

 muriatic acid, and heated to boiling. The acid 

 extracted 4 or 5 per cent, of oxide of iron; but the 

 residue still retained some colour, though it was 

 evidently whitened. This sort of clay, therefore, 

 is rather abundant in iron, and might, in certain 

 circumstances, become clay iron stone. 



