1918] Davis: The Radiolarian Cherts of the Franciscan Group 327 



ITALY™ 



Eadiolarian cherts occur in Liguria, Tuscany and on the Island 

 of Elba. Pantelli states that the radiolarian jaspers of Tuscany are 

 found in the Triassic, Cretaceous and Eocene. The jaspers on the 

 Island of Elba are referred to the Eocene. Parona and Roverto de- 

 scribe jaspers which are believed to be Permian. 



The Italian jaspers are intimately associated with serpentines, 

 gabbros, diabases and variolites. They are also associated with glau- 

 cophane and other amphibolitic schists. Some of the igneous rocks 

 are certainly extrusive and Lotti describes sections in which diabases 

 are intercalated with jaspers in perfect conformity. There appears 

 to be some dispute about the nature of the serpentine. Bonney 79 

 describes intrusive contacts of serpentines, but other workers seem to 

 have regarded them as extrusive, and Pantelli 80 states confidently 

 that he has proved the serpentines to be submarine lava flows. 



The jaspers are ordinarily red, but various other colors occur. 

 Green jaspers are next to red in order of abundance, while brown, 

 yellow, violet, white and gray varieties are found. They are associ- 

 ated with siliceous argillites (galestri) that show all variations from 

 hard compact varieties to varieties which are soft and easily broken 

 down by the action of the weather. Siliceous limestones also occur 

 with the jaspers. The jaspers contain deposits of manganese oxide. 



They are well stratified in thin layers rarely exceeding five centi- 

 meters in thickness. The jasper layers are separated by argillaceous 

 and (very rarely) by calcareous material. They are cut by numerous 

 veins of quartz which, in general, stand nearly normal to the planes 

 of stratification. They may reach a total thickness of several hun- 

 dred meters. 



In thin section, the jaspers show numerous radiolaria which appear 

 as clear colorless areas within a matrix of iron stained silica. Rarely 

 iron oxide appears within the radiolarian skeleton. The matrix con- 

 sists of a mixture of amorphous and crystalline silica, colored by 



78 Pantelli, D., I diaspri della Toscana e i loro fossili, Atti del. R. Accad. dei 

 Lincei, vin, 35, 1880. 



Lotti, B., Diaspri e ftaniti: Capitolo xrv. Descrizione geologica dell 'isola 

 d'Elba. Memorie descrittive della carta geologica d 'Italia, n. Rome, R. Ufficio 

 Geologico, 1886. 



Parona. C. P., Sugli schisti silieei a radiolarie di Cesana presso il Monginevra, 

 Atti del. R. Accad. del. Sci. di Torino, xxvn, 305, 1892. 



Parona and Roverto, Diaspri permiani a radiolarie die Montenotte, ibid., 

 xxxi, 167, 1895. 



7» Bonney, T. G., Notes on some Ligurian and Tuscan Serpentines, Geol. Mag 

 vol. 16, p. 362, 1879. 



so Pantelli, op. ext., pp. 37, 64, 65. 



