18 FIELD GEOLOGY. 



some kind a small x will do marked on the map 

 where the rock is exposed, that is, at the pond. 



Proceeding along the road to the N". we find an old 

 pit, nearly overgrown, which turns out to have been 

 formerly worked for sand. By picking about in all 

 likely places we discover that sand is not the only thing 

 in the pit, for its upper part on the S. side is really in 

 chalk. We clear away the soil with our pick, making 

 a clean-cut trench, and soon get an actual junction of 

 chalk and sand, the former overlying the latter. This 

 is a grand find, and one that will not frequently be made 

 in practice as sand-pits are made for the sake of sand 

 only, and chalk-pits for the chalk it happens rarely, 

 and tlien by accident, that pits and quarries are opened 

 on the line of junction. On the map we indicate the 

 occurrence here of chalk over sand, by the chalk sym- 

 bol x over another (for instance e) for sand, with a short 

 line between : thus -. 



Note. The method of observation, and the notes 

 made of this and other exposures of the rocks, and 

 of facts relating thereto and otherwise obtained, are 

 described in Part II. 



The boundary of the chalk of course passes through 

 this pit ; accordingly we draw a short line across the road 

 in that position, and which will be presently prolonged. 

 We now continue our walk in the same direction, but 

 see nothing worthy of remark except that clay is visible 

 in a newly-cut ditch about half-way down to the brook 

 this is indicated by another symbol, x, at the spot 

 where it is observed. Evidently we have come off the 

 sand, but nothing as yet points out the line of boun- 

 dary, and its discovery may be for the moment deferred. 



