HlNDE-1 



Radiolarian Chert. 



237 



the central test is somewhat triangular in outline, with three large 

 spines (Figs. 12, 13), resembling a Jurassic species named by Dr. 

 Rust, Tripocyclia trigonum. In another, the central portion of the 

 test is subquadrate, and from it four broad arms extend diagonally 

 (Fig. 14). This has a general resemblance to some fossil forms of 

 Hagiastrum, Hasckel. The suborder Cyrtoidea, Haeckel, is numer- 

 ously represented, and the conical turreted examples of the genus 

 Dictyomitra, Zittel (Figs. 15, 16, 17), are the best preserved and most 

 characteristic radiolaria occurring in these rocks. There are also a 

 few forms of the allied genera Litliocampc, Ehrenberg, and Setho- 

 capsa, Haeckel (Figs. 18, 19). It is fairly certain that examples of 

 many other genera besides those mentioned are present in the rocks, 

 but they are too indistinct to allow of identification, and the only 

 chance of obtaining further knowledge of these, rests on the discov- 

 ery of nodules or other portions of the beds in which the organisms 

 are better preserved. 



The forms which can be thus imperfectly identified are too few 

 to permit of any satisfactory comparison with the fossil radiolaria 

 from other localities. The character of the rock and the mode of 

 preservation appear to be very similar to what is met with in the red 

 radiolarian jaspers and cherts of Jurassic and Cretaceous age, which 

 have been described by Dr. Rust* from the Tyrol, Switzerland 

 Hungary and other places. Thus, for instance, in the upper 

 Jurassic or Tithon beds of Allgiiu in the Tyrol, there are red jaspers, 

 filled, like these Angel Island red cherty rocks, with radiolaria, so 

 that Riist compares them with the radiolarian mud brought up 

 from the greatest ocean depths by the Challenger. A r eiy similar 

 red rocks have also been described by Pantanelli in Tuscany,| and 

 by Dr. C. P. ParonaJ from Cesana, but the geological age of these 

 rocks is not yet established. There is a very considerable resem- 

 blance in the Cesana rock, as also in the mode of preservation, and 

 the general character of the radiolaria in it, with the Californian 

 Angel Island material. The radiolaria from Cesana were considered 



*Palseontographica, Bd. XXXI, 1885, Bd. XXXIV, 1888. 

 tl. Diaspri della Toscana e i loro fossili. Accad. d. Lincei. Mem. 1S80. 

 JSugli Schisti Silicei a Radiolarie di Cesana. R. Accad. Scienze di Torino, 

 XXVII, 1892. 



