APPENDIX. 



NOTE ON THE RADIOLARIAN CHERT FROM 

 ANGEL ISLAND, 



AND FROM 



BURI-BURI RIDGE, SAN MATEO COUNTY, CALIFORNIA.* 



BY 



George Jennings Hinde, Ph. D. 



Both the red, jaspery rock from Angel Island and the light col- 

 ored rock from the Buri-buri Ridge are crowded with radiolaria, 

 and, though in external appearance these rocks differ considerably 

 from each other, the character and mineral condition of the organ- 

 isms of which they are mainly composed are similar in both. In 

 the red rock from Angel Island no traces of the minute radiolaria 

 can be distinguished, even with a strong simple lens, on freshly frac- 

 tured surfaces, but where a very thin section of the rock is examined, 

 these organisms appear in transmitted light as small, clear, transpar- 

 ent dots, mostly with rounded contours, thickly imbedded in the 

 red matrix. Under the microscope these transparent bodies are 

 seen to be without any definite walls of their own, and for the most 

 part without any traces of structure, and their outlines are only 

 marked, in what appear under high powers as indistinct and indefi- 

 nite boundaries of the reddish matrix. As a rule, these bodies show 

 only the solid infilled casts of the originally hollow organism; the 

 latticed walls surrounding the hollow, have apparently been indis- 

 tinguishably merged into the clear microcrystalline silica of which 

 the cast is composed, and thus there is now left only an ill-defined 

 contour of the original form from which to determine its character 



*Radiolarian remains having been discovered in the cherts of the San Fran- 

 cisco peninsula by Professor Lawson and in the cherts of Angel Island by the 

 writer about the same time, chips and slides of the rock from both localities 

 were forwarded by Professor Lawson to Dr. G. J. Hinde, of London, England, 

 the well-known authority in this line of research. Dr. Hinde very kindly fur- 

 nished the present note concerning these interesting fossils. 



