312 University of California Publications in Geology [Vol. ll 



of Barbados. It is dull white with a pale yellow to pink tint. In 

 texture it is chalky with a very fine grain, being homogenous and giv- 

 ing no evidence of stratification. 



In thin section, the ground mass appears to consist of amorphous 

 silica in which are embedded the radiolarian remains, and also some 

 grains of quartz and rutile. A chemical analysis gives the following 

 results : 



99.90 



In addition to the constituents named, the rock contained a trace 

 of iron. 



Some of the diatomaceous earths of the Monterey group contain 

 important numbers of radiolarian skeletons. 



A notable deposit of this type is found in Sicily. It is one of a 

 group of Tertiary deposits of diatomaceous earth, found in the region 

 of the Mediterranean Sea, in Sicily, Calabria, Greece and Africa. It 

 is known as tripoli or tripolite from its occurrence in Tripoli in North 

 Africa. 49 



Emil Stohr 50 has investigated the deposits in Sicily. There are 

 numerous localities where tripoli occurs in the province of Girgenti, 

 but at the locality of Grotte, it is particularly rich in radiolarian 

 remains. The tripoli lies beneath the sulphur beds of Sicily. It is 

 less than a meter thick, but is very persistent and easily recognized. 

 The tripoli is exceedingly light, is laminated, is nearly white in color, 

 soft and easily reduced to a powder. Occasionally the beds are so 

 solid that they will ring with a blow of the hammer. Sometimes they 

 are impregnated with sulphur, and always they are more or less 

 impure by reason of the admixture of lime and clay. It contains 

 numerous fish scales and foraminifera in addition to the remains of 

 siliceous organisms. Stohr came to the conclusion that this was a deep 

 sea deposit, because of the foraminifera which appeared to be deep 

 sea forms. 



40 Haeckel, E., Report of the Scientific Eesults of the Exploring Voyage of 

 H. M. S. " Challenger. ' ' Zoology, vol. 18, pt. 1, Report on the Radiolaria. 



so Stohr, E., Die Radiolarienfauna der Tripoli von Grotte Provinz Girgenti 

 in Sicilium. Paleontographica xxvi, 71, 1879-80. 



Si0 2 

 AL0 3 



Loss on ignition 



84.20 

 10.70 

 5.00 



Diatomaceous Earths Containing Radiolaria 



