1918] Davis: The Radiolarian Cherts of the Franciscan Group 343 



CONTRIBUTIONS OF EARLIER WORKERS IN CALIFORNIA 

 TO THE QUESTION OF THE ORIGIN OF THE 

 RADIOLARIAN CHERTS 

 The first description of the radiolarian cherts of the Franciscan 

 group was written by Lieutenant Edward Belcher, 101 who visited the 

 port of San Francisco during a voyage extending over the years 

 from 1825 to 1839. In his notes, published over ten years afterwards, 

 the following description appears : 



The appearance of the jasper, at its contact with the sandstone, is often 

 very remarkable. The jasper appears not to have acted on or displaced the 

 sandstone; its exterior for eighteen inches or two feet is usually rugged and 

 mixed with carbonate of lime, quartz, and indurated clay; its interior, how- 

 ever, presents a very beautiful wavy disposition of the component laminae, 

 a remarkable example of which occurs at Needle Bock. ... It resembles an 

 immense mass of sheets of paper, or bands of list, crumpled and contorted by 

 lateral pressure. This contortion only occurs in the red jasper, the yellow 

 being seldom (if at all) stratified, but generally separated by cracks into 

 rhomboidal pieces. 



In the year 1849, James D. Dana 102 published his description of 

 the geology of the regions visited by him during the Wilkes Expedi- 

 tion. He describes the cherts occurring near Sausalito and San 

 Francisco and states that they are subordinate members of the "tal- 

 cose rock formation. ' ' 



Dana divides the rocks of northern California and Oregon into 

 groups, the oldest of which he refers to as the "Ancient Plutonic 

 Series. ' ' He states that the various members of this division are inti- 

 mately associated with one another and belong to a single series. 

 This division includes granitic rocks occurring in northern Cali- 

 fornia, which are said to grade into talcose rocks, while hornblende 

 rocks and serpentine are the intermediate members in the transition. 

 He believes that the talcose rocks in their turn pass into "prasoid 

 rocks" and these into jaspers. In the "Shasty Mountains" (Kla- 

 math Mountains), Dana describes some very soft talcose rocks which 

 he believes show transitions to a homogenous siliceous rock with a 

 smooth conchoidal surface. He describes it as follows : 



This greenish rock would be called prase in hand specimens, and is often 

 more or less translucent, with a smooth conchoidal fracture. It is very 

 siliceous, consisting probably of silica and feldspar, with a trace of coloring 



ioi Zoology of Captain Beechey 's Voyage, London, 1839. 



i° 2 Beport of the United States Exploring Expedition during the years 1838- 

 1842: X, Geology by J. D. Dana, Philadelphia, 1849 



