UPPER GREENSAND. 393 



The Chert-beds which form the high grounds west and south-west of Chard are 

 generally much broken up on the surface, the soil is often a drift-clay with angular 

 stones, and it becomes wet and boggy in many places. The sands are not usually 

 fertile, and much of the country occupied by them is covered with plantations of fir, 

 or with gorse and heather. 



Blackdown Beds. — During the past 50 years much attention has 

 been paid to the fossils obtained from the sands with hard con- 

 cretions, exposed at the whetstone pits of Blackdown, which is a 

 projection of the Blackdown Hills west of Dunkeswell, in Devon- 

 shire. Whetstones or scythe-stones have been worked for many a 

 year in the escarpment between Blackborough Hill and Hembury 

 Fort, including Punchey Down and Upcott Pen, near Kentisbere and 

 Broadhembury. Indeed, as pointed out by the Rev. W. Downes, 

 so extensive have been the burrowings or tunnels driven into the 

 hills for the purpose of working the stone, that considerable 

 subsidences have occurred, whereby Blackborough (or Mortal Pen 

 Beacon) has lost quite thirty feet of its height.^ Hence 

 opportunities have occurred for obtaining large collections of 

 fossils from the sands. These are preserved in chalcedony, and 

 being derived from sands beneath the Chert beds (which have been 

 denuded), the 'Blackdown fauna' represents only a part of the 

 Upper Greensand of the district, and the term Blackdown Beds is 

 similarly restricted. 



The exact age of these strata has formed the subject of consider- 

 able dispute among palaeontologists, inasmuch as representatives 

 not only of Upper Greensand, but also of Gault and even Lower 

 Greensand, have been considered to be present. The Blackdown 

 Beds were described long ago by Fitton, and the age of the fossils 

 has been discussed by D. Sharpe,- Godwin-Austen, E. Renevier,^ 

 and others, and more recently by the Rev. W. Downes. 



The Upper sands at Blackdown, according to Mr. Downes, are 

 characterized by Pecten quadricostatiis, then come sands with 

 Pcctuncuhis siiblcBvis and Trigotiia affinis [excen/rica) ; beneath in a 

 bed called the " Red rock," Cyprina cuneata and Exogyra conica are 

 abundant ; lower down Tiirritella granidata, and Siphonia iidipa 

 {pyriformis) are found ; while Pectunculus iimbo7iatus, Trigonia 

 a/cBfor?nis and Inoceramiis sulcafiis occur more or less plentifully in 

 the lowest beds. Mr. Downes concludes that we do not find 

 exclusively Upper Greensand fossils at the top of the series, Gault 

 fossils in the middle, and Lower Greensand forms at the base, and 

 on the whole it is best to regard the Blackdown Beds as Upper 

 Greensand, restricting the term Gault to the clay wherever it occurs 

 below that Greensand.^ 



The scythe-stones or whetstones are known also as Devonshire Batts, and in 

 Dorsetshire as Rubber-batts or Balkers. Dr. Fitton remarked that the strata 



' Trans. Devon Assoc. 1880. 

 ~ Q. J. X. 186. 



^ Bull. Soc. Vaudoise des Sc. Nat. v. 51 (Q.J. xii. part 2, p. 21) ; see also 

 Barrois, L'age des couches de Blackdown, 1875. 

 * Q. J. xxxviii. 75, xli. 27. 



