UPPER PORTION OF DUNDRY HILL. 223 



than those built on the lowest beds of the limestone only 

 a little above the level where springs are thrown out by the 

 underlying clays. Of late the tendency has been to build 

 detached farmsteads and cottages on the slopes formed of 

 the Pliensbachian clays, instead of, as of old, on the sum- 

 mit-level of the Hill. Although there are manifest advan- 

 tages as regards shelter and facility of haulage in these 

 positions over the higher levels, we consider the heavy 

 character of the subsoil and the necessity of trusting to 

 spring water render these sites less suitable from a health 

 standpoint than those indicated by us above the level of the 

 escarpment. 



X. The Map of Dundry Hill. 



This communication is accompanied by a map, on the 

 scale of 3 inches=l mile, to indicate the age of the different 

 deposits and their superficial extent as found by us to obtain 

 at Dundry Hill. As the map of the Geological Survey 

 shows round so very much of the hill the Marlstone of the 

 Middle Lias, and even beds below that, coloured as if they 

 were Inferior Oolite, our map is, we consider, of value in 

 that it amends the official document. Bat we claim that 

 it is of importance in another respect. If the maps of the 

 Geological Survey be taken, and the upper line of the 

 Upper Lias be followed through the counties of Gloucester, 

 Dorset, and Somerset, it will be found to mark a purely 

 physical feature — the place where clay is overlain by sand, 

 which can readily be followed because it is shown by the 

 outburst of springs, and by a change of surface configura- 

 tion. This method of mapping is based on the assumption 

 that changes of sediment and changes of fauna were practi- 

 cally synchronous ; but that assumption has been so often 

 disproved by palaeontological research ; and it has been shown 



