150 ROCK STRATA 



iron ; the top rock, treated in like manner, loses 

 only 1 or 2 per cent, in weight, and the acid 

 extracts only a trace of iron and of alumine. 

 The colour of the residuary sand, in both cases, 

 is not materially altered -, which makes it proba- 

 ble, that the sand is combined with the alumine. 



The bottom rock is harder, and better cement- 

 ed together, than the top, as might be expected 

 from what has already been stated ; it must, I 

 presume, be much better adapted for buildings, 

 than the latter, which, when imbued with water, 

 is softened so as to fall almost by its own weight. 



2. Sand- Rock, at Mr, Knowless Coal- Pit, 

 near Agecroft Bridge. 



This sand-rock is found 15 yards below the 

 surface, and is many yards thick. Its specific 

 gravity is 2.47 ; it acquired 2 or 3 grains per 

 cent, by being immersed in water. It agrees, 

 very nearly, in its constitution, with the upper 

 part of the Colly hurst rock ; it has some horizon- 

 tal streaks in the fracture, which arc said to be 

 characteristic of vicinity to coal. 



