308 University of California Publications in Geology [Vol. 11 



globigerina marls, into a set of passage beds which comprise white 

 chalky calcareo-siliceous earths. From these passage beds, there is a 

 continuous gradation upward into whiter and more siliceous beds of 

 much lower density, which are composed largely of the skeletons of 

 radiolaria. In Trinidad, the globigerina marls are 120-140 feet thick 

 and the radiolarian earths are 40-50 feet thick. 



The radiolarian marls here often show scales with pearly luster, 

 which represent the fragments of the frustules of diatoms. Some of 

 the marls contain as much as twenty per cent of these. The deposits 

 of Trinidad contain more quartz and argillaceous matter than those 

 of Barbados, apparently being laid down closer to land. The radio- 

 larian earths also contain more calcium carbonate, some of them 

 running as high as twenty per cent. The foraminifera of these marls, 

 according to Guppy, are those which are found now in deposits in 

 depths of 1000 fathoms. 



Similar siliceous earths are found at other points throughout the 

 same general region. Radiolarian earths are said to occur in the 

 island of Hayti, 44 and deposits like the Barbados earths occur at 

 Baracoa, in Cuba, 45 where they are reported to have the same rela- 

 tions as do the rocks of Barbados. 



In Jamaica, no radiolarian earths are known, but a white lime- 

 stone — the Montpelier White Limestone — is regarded as a deep sea 

 deposit. It is free from terrigenous material and contains no mol- 

 luscan remains or shallow water corals. 



Radiolarian Mudstones 

 IN GONDWANA SEEIES 



As illustrations of radiolarian rocks of the second class, there 

 might be mentioned certain shales in the Gondwana series of India. 48 



The Upper Gondwana series, near Madras, is divided into two 

 groups. The lower group is called the Sripermatur group, and con- 

 sists of two formations. The upper formation is composed of thin 

 bedded, pale, buff colored or white shales, containing plant remains. 

 It is ten feet thick. The lower formation is composed of sandstones, 

 grits, and micaceous sandy shales which attain a thickness of fifteen 

 feet. The upper shales contain plant remains and some marine fos- 



Quar. Jour. Geol. Soc, vol. 48, p. 219, 1892. 

 « Gregory, J. W., Quar. Jour. Geol. Soc, vol. 51, p. 293, 1895. 

 ■*o Coomaraswamv, A. K., Occurrence of Radiolaria in the Gondwana Beds 

 near Madras, Geol. Mag., vol. 39, p. 305, 1902. 



