332 Reports and Proceeding s^ 



matter from its solution' in water charged with carbonic acid, tvliich 

 is a known solvent of the phosphate ; an analysis of the matrix 

 has j)roved that phosphate of lime is appreciably present in it. The 

 author doubted the derivation of the nodules from the denudation of 

 the subjacent Gault, and exhibited a collection of these to show that 

 they were distinguished by more stunted growth. 



The deposit was on the whole considered to represent the thin 

 band with similar fossils at the base of the Chloritic Marl, as seen in 

 the west of England, in which district it is underlain by the true 

 arenaceous Greensand. The absenoe of the trae Greensand was 

 attributed to the intervention of the old palaeozoic axis of the London 

 area ; and it was finally suggested that a similar axis might stretch 

 from Leicestershire to Harwich, causing the change in character of 

 the Lower Cretaceous beds between Cambridgeshire and Norfolk. 



3. " Some Observations on the tipper Greensand Formation of 

 Cambridge." By W. Johnston Sollas, Esq., Assoc. Eoyal School of 

 Min-es, London. Communicated by the Eev. T.- G. Bonney, M.A., 

 E.G.S. 



The Greensand Formation consists around Cambridge of a Chalk 

 marl containing harder portions of a different nature disseminated 

 throughout it, these are separated from the Chalk Marl by levi- 

 gation, and sorted by sifting into larger bodies, consisting almost, 

 entirely of the so-called "coprolites," and smaller bodies — the so- 

 called " Greensand." The author gave a general account of his con- 

 clusions regarding the " coprolites," reserving details for a future 

 communication. Of all the facts the most obvious is the connexion 

 between presence of " coprolite," and former existence of organic 

 matter ; when coprolite is found incrusting a bone or other fossil, it 

 is precisely on those parts where animal matter adhered most 

 abundantly. Instances were cited, as in Palceoeorystes, where the 

 absence of animal matter on the back of the carapace is marked by 

 an absence of phosphatic incrustation ; while the sternal side, where 

 animal matter could easily escape, is often altogether embedded in 

 " coprolite." Coprolites are the fossilization of organic matter derived 

 from very vaiious sources. In many cases they owe their origin to 

 sponges, almost certainly so in the case of cylindrical coprolites per- 

 forated by a cylindrical cavity, now filled up with Chalk Marl ; 

 other forms have an allied origin. Thus coprolites are the flints of 

 the Gault. The Greensand is a mixture of calcareous, siliceous, and 

 dark-coloured grains of uncertain chemical composition. The cal- 

 careous grains consist of sponge spicules, minute shells, fragments 

 and prisms of shell substance, bivalve entomostraca, microsopic 

 corals, minute echinoderm species, polyzoa, and foraminifera. A list 

 was given of the Foraminifera, the abundant occurrence of Lagena 

 here being particularly noticed, as, with the exception of X. apiculata, 

 mentioned by Eeuss, the genus had not before been noticed below 

 the Maestricht Chalk. The siliceous grains consist of fragments of 

 various rocks, some of volcanic origin. The dark coloured grains are 

 coprolitic debris and true green grains. Tlie green grains are almost 

 all casts of Foraminifera, derived chiefly from Bulimina ; others are 



