56 MM. Reid and Sharman — 



accept this determination. Mr. Teall, 1 writing in 1873, points out 

 the close relation of the fossils from the " Coprolite Bed " of West 

 Dereham to those of the " Ammonites mammillaris zone " of Folke- 

 stone, and correlates the overlying blue marly clay with the Gault, 

 from the occurrence in it of Ammonites interruptus. 2 



However, during the Geological Survey of this neighbourhood, 

 great difficulty was found in separating the so-called " Gault " from 

 the Chalk Marl, and after a minute examination of the whole district, 

 the only boundary-lines which could be traced were, a distinct 

 line of erosion below the " Coprolite Bed," and a lithological line 

 where the hard Chalk rests on the Chalk Marl. Though close 

 search was made for the more or less phosphatic bed which in many 

 other parts of England marks the base of the Chalk, no trace of it 

 could be found, and the conclusion could not be avoided, that the 

 so-called Gault was both lithologically and stratigraphically merely 

 part of the Chalk Marl. 



The new Coprolite Works lately opened at West Dereham show 

 the best sections of the Phosphate Bed, and of the Marl immediately 

 overlying it ; but the Marl there is very thin, being partly cut out 

 by Boulder-clay. In October, 1883, the section seen in the well was : 



Ft. in. 

 ( 5. Boulder-clay, very chalky 7 



Chalk. Marl < 4. Blue M arl, drying bluish white ... ... 4 



( 3. Coprolite Bed 9 



■vr „ .„ ( 2. Hard loamy nodular Greensand 2 



JNEOCOMIAN ... { , t> ■ J j 



( 1. Bunning Band 

 The other parts of the works are on lower ground, and show less 

 Boulder-clay ; though the Marl is about the same thickness, except in 

 one place, where Boulder-clay cuts through it into the Greensand, 

 and in other parts where the Coprolite Bed approaches the surface. 



Taking the beds in order, No. 1 is undoubtedly Neocomian, 

 though here it has yielded no fossils. No. 2 is probably also 

 Neocomian, which has been slightly disturbed, reconstructed during 

 the deposition of the overlying beds, and subsequently hardened by 

 infiltration. 



No. 3 is the bed for which the deposit is worked. It consists of 

 a mass of phosphatic nodules in a greenish loamy or sandy matrix, 

 partly derived from the underlying Neocomian Beds. Mixed with 

 and occasionally imbedded in the nodules are numerous fossils. 

 These fossils seem to be mainly derivative, for though most of them, 

 as Mr. Teall has pointed out, belong to the zone of Ammonites 

 mammillaris, there is apparently also an occasional admixture of 

 older and newer forms, including some species, such as Dentalium 

 ellipticum, probably belonging to the Gault. 



The " Coprolite " occurs in this bed in two forms. The more 

 abundant is a poor sandy phosphate in irregular nodules, which may 

 have been partly formed in the bed itself. These seldom contain 

 fossils. The associated mollusca are generally either loose casts, or 

 are imbedded in a sandy matrix which has not been phosphatized, 



1 The Potton and Wicken Phosphatic Deposits, 8vo. pp. 20, 21. 



2 See also Keeping's Neocomian Deposits of Upware, etc., 8vo. pp. 11, 54. 



