694 MR. W. M. HOLMES ON RADIOLARIA PROM THE [NOV. I9OO, 



36. On Radiolaria from the Upper Chalk at Coulsdon (Surrey). 

 By W. Murton Holmes, Esq. (Communicated by W. Whitakbr, 

 Esq., BJl., E.R.S., E.G.S. Head June 20th, 1900.) 



[Plates XXXYII & XXXVIII.] 



The occurrence of radiolaria in the Chalk of this country is suffi- 

 ciently rare to call for some notice, and the present paper has been 

 written at the suggestion of Mr. William Hill, E.G.S., who saw some 

 of my specimens. As was suggested by Messrs. Hill & Jukes- 

 Browne in their paper on Chalk radiolaria, 1 one would have expected 

 the physical conditions of the Upper Cretaceous period to have been 

 more favourable to the existence of such organisms than those of the 

 Lower Cretaceous or of Jurassic times, in the rocks of which periods 

 radiolaria are not uncommon on the Continent. 



One reason may be that, as in recent deep-sea dredgings, we find 

 the ooze in some instances to contain radiolaria in considerable 

 numbers, while in others they are either entirely absent or very 

 scarce ; so it is possible that in certain tracts of the Chalk there 

 were no radiolaria present when that was deposited. Again, the 

 ready solubility of radiolarian tests, more especially when in contact 

 with carbonate of lime, will account for the disappearance of large 

 numbers. 



Dr. Cayeux 2 has given a summary of the papers which been have 

 published on Cretaceous radiolaria. 



Prof, W. J. Sollas found some in the Cambridge Greensand in 

 1873. These, however, were not described. Geheimrath K. von 

 Zittel found in 1876, in the Upper JSenonian of Northern Germany, 

 six species of radiolaria belonging to four known genera. Signor 

 Pantanelli in 1880 noted the presence of one species in the Creta- 

 ceous of Tuscany. The late Dr. Wallich, in 1883, recorded the 

 presence of four genera (Astromma, Haliomma, both discoidal and 

 spherical, and Podocyrtis) in the cavities of hollow flints from some 

 Surrey gravel-pits. The exact horizon of these could not be deter- 

 mined. Dr. 11 iist has figured only two species from the Upper Chalk 

 of England, Dictyomitra angliea and Dictyospiris chlamydea (quoted 

 by Messrs. Hill & Jukes-Browne). Prof. Eritsch mentions, in his 

 studies on Bohemia (1893), eleven species, belonging to nine genera, 

 in the marly beds of Priesen (Lower Senonian). Dr. Deecke dis- 

 covered, in 1894, radiolaria in Chalk-flints at Riigen. 



Messrs. Hill & Jukes-Browne have observed many form3 in the 

 Melbourne Rock, 1895 (op. cit.). Erom the smectite of Battice, 

 near Herve, Belgium, in the horizon of Belemnitella quadrata, 

 Dr. Cayeux has described (op. cit.) radiolaria belonging to twenty- 

 seven genera. He notices the great predominance of the order 

 Discoidea, and especially of the family of Porodiscidse. 



1 Quart. Journ. Geol. Soc. vol. li (1895) p. 600. 



2 ' Etude micrographique des Terrains sedimentaires ' 1897, p. 185. 



