FRANCISCAN GROUP 



11 



miners, it has been more thoroughly studied than any 

 of the younger formations in the district, and is 

 therefore described in more detail. 



All the rocks of the Franciscan group in the New 

 Almaden district show at least incipient metamor- 

 phism in some places, but most of the rocks of the 

 group are so little changed that in the field they appear 

 unmetamorphosed. The typical rocks do not show 

 slaty cleavage, foliation or schistosity, prominent de- 

 velopment of stress minerals, or crystalloblastic tex- 

 tures. In a few areas of relatively small extent, how- 

 ever, some of the rocks of the group are crystallo- 

 blastic, schistose, or even gneissic, having obviously 

 been subjected to special metamorphic processes that 

 have not affected the rest of the group. These dis- 

 tinctly metamorphosed rocks consist largely of schist, 

 amphibolite, and crocidolite-bearing metachert, prob- 

 ably formed from the normal graywacke, greenstone, 

 and chert. Because of their unusual and seemingly 

 erratic distribution, these metamorphosed rocks of 

 the Franciscan group are usually discussed together, 

 rather than treated separately as special metamorphic 

 phases of the various rocks from which they are de- 

 rived, and they will be discussed together in this 

 report. These metamorphosed rocks have attracted 

 a disproportionate amount of attention because of the 

 interest aroused by a few uncommon minerals found 

 in them, and this, together with the fact that the 

 group was referred to in early reports as the Meta- 

 morphic series, has led to a widespread but erroneous 

 belief that the Franciscan group consists largely of 

 crystalline schists. 



The name Franciscan (series) was first used by 

 Andrew C. Lawson (1895a, p. 342-356; 1895b, p. 399- 

 476), and it has been adopted by all geologists work- 

 ing in the California Coast Ranges. Other names, 

 however, had previously been applied in several im- 

 portant publications to rocks now included in the 

 Franciscan group. As early as 1856, Blake (p. 153) 

 used the name San Francisco or California sand- 

 stone in a report containing a description and map of 

 the sandstone around San Francisco Bay. Nine years 

 later Whitney (1865, p. 19-108) described the entire 

 group, together with the serpentine, using the terms 

 San Franciscan sandstone, metamorphic rocks, and 

 metamorphosed Cretaceous. Becker (1888) applied 

 various terms, including Neocomian, Metamoprhic 

 series, and Knoxville, to the rocks older than the Chico 

 (Upper Cretaceous) formation of the Coast Ranges. 

 Since these early studies a great many reports deal- 

 ing directly or indirectly with the Franciscan group 

 have appeared. 



BIBLIOGRAPHY OF THE FRANCISCAN GROUP 



General 



1855 Blake, W. P., Observations on the characters and prob- 



able geological age of the sandstone formation of 

 San Francisco : Am. Assoc. Adv. Sci. Proc., v. 9, 

 p. 220-222. 



1856 Blake, W. P., Report of explorations in California for 



railroad routes: 33d Cong., 2d sess., Ex. Doe. 78, 

 Geol. Kept., p. 153. 



1858 Blake, W. P., Report of a geological reconnaissance in 

 California : New York, H. Bailliere, p. 145-159, map 

 facing p. 145. 



1865 Whitney, J. D., Geological survey of California : Geol- 

 ogy, v. 1, p. 19-108. 



1885 Becker, George F., Notes on the stratigraphy of Califor- 



nia : U.S. Geol. Survey Bull. 19, p. 7-25. 



1886 Becker, George F., Cretaceous metamorphic rocks of 



California : Am. Jour. Sci., 3d ser., v. 31, p. 348-357. 

 1888 Becker, George F., Geology of the quicksilver deposits 

 of the Pacific slope: U.S. Geol. Survey Mon. 13, 

 p. 1^86. 



1892 Fairbanks, H. W., The pre-Cretaceous age of the meta- 



morphic rocks of the California Coast Ranges : Am. 

 Geologist, v. 9, p. 153-166. 



1893 Fairbanks, H. W., Notes on a further study of the pre- 



Cretaceous rocks of the California Coast Ranges: 

 Am. Geologist, v. 11, p. 69-84. 



1895 Lawson, A. C., A contribution to the geology of the Coast 

 Ranges : Am. Geologist, v. 15, p. 342-356. 



1895 Lawson, A. C., Sketch of the geology of the San Fran- 

 cisco Peninsula : U.S. Geol. Survey 15th Ann. Rept., 

 p. 399-^76. 



1904 Fairbanks, H. W., Description of the San Luis quadran- 

 gle [California] : U.S. Geol. Survey Geol. Atlas, Folio 

 101, p. 2-3, 9. 



1909 Branner, J. C., Newsom, J. F., and Arnold, Ralph, De- 



scription of the Santa Cruz quadrangle, California: 

 U.S. Geol. Survey Geol. Atlas, Folio 163, p. 2, 8-11. 



1910 Smith, J. P., The geologic record of California: Jour. 



Geology, v. 18, p. 216-227. 



1914 Lawson, A. C., Description of the San Francisco district : 

 U.S. Geol. Survey Geol. Atlas, Folio 193, p. 4-7, 17, 

 19, 22. 



1933 Reed, R. D., Geology of California : Am. Assoc. Petro- 

 leum Geologists Spec. Pub., p. 27-59, 72-97. 



1936 Reed, R. D. and Hollister, J. S., Structural evolution of 

 Southern California : Am. Assoc. Petroleum Geolo- 

 gists Spec. Pub., p. 55-57. 



1943 Taliaferro, N. L., Geologic history and structure of the 

 Central Coast Ranges of California : California Div. 

 Mines Bull. 118, pt. 2, p. 119-162. 



1943 Taliaferro, N. L., Franciscan-Knoxville problem : Am. 

 Assoc. Petroleum Geologists Bull., v. 27, no. 2, p. 109- 

 219. 



1946 Allen, J. E., Geology of the San Juan Bautista quadran- 

 gle, California: California Div. Mines Bull. 133, 

 p. 22-26. 



1948 Huey, A. S., Geology of the Tesla quadrangle, Califor- 

 nia: California Div. Mines Bull. 140, p. 14-23. 



Sandstone 



1918 Davis, E. F., The Franciscan sandstone: California 

 Univ., Dept. Geology Sci. Bull., v. 11, p. 6-16. 



