1918] Davis: The Radiolarian Cherts of the Franciscan Group 325 



THE ALPS 



In the Upper Jurassic, at many places in the Austrian Alps, the 

 Tyrol, Switzerland, Hungary, and Servia, there are radiolarian 

 cherts. 71-72 



Rust distinguishes between jasper and hornstone. In the term, 

 hornstone, he includes light to dark gray to black rocks composed of 

 cryptocrystalline silica. The jaspers are rocks consisting of a mixture 

 of fine white, or iron stained red, brown, and yellow clay, with silicic 

 acid. While these rocks appear as definite types, there are transitions 

 between them. Both types of rocks in these regions contain calcium 

 carbonate. The hornstone contains lime carbonate as a fine powder 

 and also as calcite rhombs. The jaspers contain lime carbonate in 

 fine white crystalline bands. Often they contain radiolaria in such 

 large numbers that the tests lie against each other, the interstitial 

 spaces being filled with the clay-iron-silica mixture. In the hornstone 

 the remains of radiolarians are only occasionally found, but they 

 show sponge spicules in greater abundance than the jaspers. 



Hahn 73 describes the cherts as consisting of layers of siliceous rock 

 of an intense blood red color, or more rarely, of greenish color, which 

 are interbeclded with dense brown red, or greenish gray quartzose 

 and argillaceous marls. The total thickness of these beds is from 

 ten to twenty-five meters. Under the microscope the cherts are seen 

 to be filled with radiolaria. Radiolaria are not so commonly pre- 

 served in the argillaceous layers, but the cherts contain many well 

 preserved forms. These rocks are believed by Hahn to represent the 

 present radiolarian oozes of the deep sea, such as now accumulate 

 at depths between 3000 to 7000 meters. 



In his description of the Davos Valley, in Switzerland, A. V. 

 Jennings 74 refers to radiolarian cherts associated with red shales. 

 They occur as lenticular bodies in shales believed to be Triassic in 

 age, and are associated with serpentine and a variolitie diabase. 



HAEZ MOUNTAINS 

 Radiolarian cherts occur at many points in the Harz Mountains. 

 They are of Lower Carboniferous age and correspond to the radio- 



7 1 Bust, Beitriige 7Air Kenntniss der fossilen Badiolarian aus Gesteinen des 

 Jura. Palaeontographiea, xxxi, 269, 1885. 



72 Hahn, F. F., Geologie der Kammerken Sontagshorngruppe I, Jahrb. d. k. k. 

 geol. Beichsanstalt, Bd. 60, Heft 2, S. 389-90, 311-420; Bd. 2, Heft 4, S. 637-712. 



73 Cited by Grabau in Principles of Stratigraphy, p. 459. 

 7 * Quar. Jour. Geol. Soc, vol. 55, p. 394, 1899. 



