82 



bitumen, but is of a very different nature. Vauquelin con= 

 siders it as sulphurated hydrogen. The colour is caused by 

 oxide of iron with more or less clay. The odour goes off 

 from the surface if exposed to the atmosphere ; which makes 

 it necessary to scrape it: the heat used in burning it to lime 

 dissipates it entirely. 



The lower Jigure is veiy interesting, as it shows the stra- 

 tification while crystallizing, the darker parts making it 

 evident. The top of this specimen is crystallized with the 

 acute, ends of the inverse rhomb, (see tab. 4. upper Jigure,) 

 pointing outwards, which is not unusual in this kind of 

 concentric construction of calcareous earths. Lady Wilson 

 first gave me specimens of this stone, from Sunderland in 

 the countv of Durham. Mr. Winch, F. L. S. has since faf 

 voured me with many varieties of it from the same place. 

 The Rev. John Harriman sent me a specimen from Hartle- 

 pool in the same county; and it should seem by his obser- 

 vations that this curious stratum may extend from Hartle- 

 pool to Sunderland, all along the coast, and perhaps much 

 farther. It is called Building Hill Stone in Sunderland. 



