298 PROCEEDINGS COTTESWOLD CLUB 1912 



The blue clay, which is so frequently exposed in excava- 

 tions in the roads in the Lansdown and Marl-Hill districts and 

 the lower slopes of Battledown, belongs to the formation called 

 by geologists, the " Lower Lias." If the topmost portion is 

 of a dirty yellow colour it is because the finely-disseminated 

 iron-pyrites (FeSJ in the clay has oxidized and become 

 hydrated. 



Tins Lower-Lias clay everywhere in the district under 

 consideration underlies the deposits of gravel, sand, etc. (figs. 

 I and 2) : they rest in hollows excavated out of the Lias clay. 



d 



I A very little consideration will make it clear that before 



^ the gravel and sand was laid down, the surface of this district 

 r was in places more undulating than it is to-day. In its deepest 

 g part the Superficial Deposit cannot be far short of 50 feet 

 I thick. On the other hand, tracts that have at the present 

 ^ time clay at the surface have undergone a considerable amount 

 ^ij I of lowering by denudation. This means that before the Super- 

 1 = ficial Deposits were laid down, the area under consideration 

 was furrowed with relatively deep valleys. Along these 

 flowed streams which sprung from the hill-sides and brought 

 down with them, and rounded in their onward progress, 

 pieces of Liassic and Oolitic limestones. It may be that as 

 ..I I these streams deepened their channels they left in sporadic 

 ^ "f fashion on their valley-sides deposits of hill-derived gravel : 

 "! it may be also that in early Glacial times more gravel than 

 ■^ formerly was swept downwards by the swollen brooks. Any- 

 how, the evidence at present to hand certainly seems to in- 

 dicate that there was gravel present in the district before the 

 yellow sand was introduced and that this gravel was rather 

 sporadically distributed. 



The yellow sand was introduced from somewhere else — 

 from a distance and not from the neighbouring Cotteswold 

 Hills, because there is and never was any deposit in those 

 hills from which it could have been derived. The sands on 

 the top of Cleeve Hill, the " Harford Sands " as they are 

 called, are much finer-grained than the yellow sands at Chel- 

 tenham. 



a 



