86 JRemeu's — JuJies-Browne /' Hill — Gcmlt and U. Grcensand. 



(in part) — the Merstliam or Devizes Beds, which are placed in thd^ 

 zone of Ammonites rostratus. The lower portions of this zone con- 

 sists of marly clays, and above these are the well-known beds of 

 Malnistone or Firestone, siliceous rocks with a considerable amount 

 of silica in the colloid state, which has been derived from the 

 spicules of siliceous sponges. This Malmstone occupies a large area 

 in the South of England estimated at nearly 4,000 square miles. 

 It extends from near Westerham, Kent, on the east, and from its 

 thickness along the western outcrop the author believes that it 

 stretched originally far to the westward over the counties of Oxford,^ 

 North Wilts, and Gloucestershire. This Malmstone passes into 

 a fine-grained micaceous sandstone. 



In the Isle of Wight and in the South- West of England, a large 

 portion of this zone of Am. rostratus consists of fine soft sands with 

 intermediate beds of hard calcareous sandstone ; in some places the 

 cemented materials take the form of oval or rounded doggers or 

 burr-stones. Again, in the Blackdown Hills of Devonshire and 

 near Stourton in Wiltshire, the sands of this zone contain siliceous 

 nodular accretions, formerly worked for whetstones, the silica in 

 which is derived from sponge remains. 



The third division of the Selbornian comprises the highest portion 

 of the Upper Greensand, and as this is most highly developed near 

 Warminster it is known as the Warminster Beds, and included iit 

 the zone of Fecten asper and Cardiaster fossarius. The zone of 

 Pecten asper near Warminster includes three sets of beds : (1) Green- 

 sand and sandstone ; (2) fine grey sand with layers and nodules 

 of chert ; and (3) a light greensand with calcareous concretions, 

 which forms the highest portion of the series and contains the 

 well-known Warminster fauna. The author states that no Ammonite 

 or other Cephalopod has yet been found in this zone which does not 

 range into the Chalk above or into the beds below. 



Pecten asper, the principal index fossil of this zone, has a wid& 

 distribution both in this country and in France. In England it has 

 been found in the Malmstone of Hampshire, that is, in the zone of 

 Am. rostratus, and occasionally it occurs in the same zone in France. 

 In the zone distinguished by its name it is found near Warminster 

 and other places in Wiltshire, also in Dorset, and the Isle of Wight. 

 It passes up into the Chloritic Marl, and occurs in the nodule bed at 

 the base of the Chalk near Chard, and in certain beds of Cenomanian. 

 age in Devonshire. In France also this species is common in the 

 ' craie glauconieuse,' the equivalent of our Lower Chalk. Its mere 

 occurrence, therefore, cannot be considered as proof that the bed 

 containing it belongs to the Upper Greensand. 



The Warminster or Pecten asper division of the Upper Greensand 

 is confined to the south-western and south-central counties from 

 the Isle of Wight to Buckinghamshire. Its maximum thickness 

 is estimated at 60 feet, but where the chert beds are not present 

 it is reduced to about 12 feet. The well-known chert beds of the 

 Undercliff in the Isle of Wight are included in this division. 



Chapters v-xxii give detailed descriptions of the varying features. 



4 



