MAPPING. 19 



We should expect to find below the Chalk, the Upper 

 Green-sand, and below this the Gault clay ; probably we 

 are now on the latter formation, but of this we cannot 

 be certain without further evidence. There is a brick- 

 yard on the other side of the brook, and the pit there 

 from which the clay is taken affords ample material to 

 justify our coming to that conclusion.* Looking north- 

 wards the gault clay forms a nearly level flat of rich 

 pasture land extending apparently beyond the margin 

 of our map. 



On retracing our steps we observe in the distance an 

 excavation of some kind, a good way off on the W. side 

 of the road, .and thereto we make our way. It proves 

 to be a trench dug for a drain, at one part of which clean 

 gault is turned out, and a little higher up, sand. The 

 junction is close by, not exactly visible anywhere, but 

 it must be between the two places, and we can here 

 commence our line. But where are we ? Away from 

 the road, the brook, and everything else on the map. 

 Now the compass comes into requisition, and we at 

 once take a bearing on the church, it reads S.E., and 

 we draw a pencil line accordingly.f Taking a second 

 bearing on the barn away to the northward, we get 

 another line crossing the first at our exact position. 

 Here then begins the line, and here also seems to be a 

 slight alteration in the slope of the ground, the gault 

 makes almost a flat to the N., the sand rises more 

 rapidly to the S., the change of feature due evidently to 

 the difference in the strata.^ Our line must be drawn 

 as nearly as may be where this change occurs, which 

 seems to very nearly follow the contour of the ground, 



* Post, p. 55. t Ante, p. 8. $ Post, p. 28. 



22 



