XIV GEOLOGICAL FEATURES 



of minute animalcules had in turn been deposited in the 

 same locality at the bottom of the ocean, and the siliceous 

 shells had been converted into layers or nodules of flint 

 before the next deposit of calcareous shells. 



There are two Chalk deposits, the Upper and the Lower. 

 T^ e ^wer Chalk contains scarcely any flints, but very 

 fcftt^' often has radiated nodules of iron-pyrites scattered through 

 it, and is generally hard. It is exposed in cuttings for the 

 railway and in chalk-pits at Lye Hill, and in other pits 

 on the borders of Pewsey Yale. Fossil Terebratulce have 

 been found at Lye Hill ; but they are much crushed and 

 broken, showing that the Chalk has been subjected to 

 very great pressure. The Lower Chalk is also exposed in 

 excavations for the foundations of a house close to the 

 College, on the right of the Bath Koad, where it is almost 

 as hard as ordinary limestone. There has been a chalk-pit 

 here, from which chalk was dug to form the Bath Road 

 when its course was altered, which has been filled in with 

 the sand and broken flint-rubble from the road ; but this 

 is interrupted about 6 feet below the surface by a band 

 of dark vegetable mould, 3 or 4 inches thick, containing 

 minute shells of Helicidce or snails, many of which are almost 

 too small to be clearly made out by the naked eye. 



The Upper Chalk, containing continuous sheets or bands 

 of flint, and also layers of flint-nodules showing the strata 

 or planes of stratification, is chiefly met with in the neigh- 

 bourhood of Marlborough. This is generally much softer 

 than the Lower Chalk. 



The Chalk hills of North Wilts lie at the western extremity 

 of the range of hills running through Cambridgeshire, 

 Hertfordshire, and Buckinghamshire, and forming the 

 northern boundary of the Tertiary deposits of the London 

 basin. These hills throw out their rounded headlands very 

 irregularly on the western side, as at Oldburj" and Morgan's 

 Hill, and on the southern side, as at St. Anne's Hill or Tan- 



