Marin County CA Archives History - Books .....Glaciology Of San Francisco Bay 1958 ************************************************ Copyright. All rights reserved. http://www.rootsweb.com/~usgenweb/copyright.htm http://www.rootsweb.com/~usgenweb/ca/cafiles.htm ************************************************ File contributed for use in USGenWeb Archives by: Joy Fisher sdgenweb@yahoo.com April 11, 2007, 1:01 am Book Title: Shark Point - High Point Glaciology of San Francisco Bay THE TIBURON PENINSULA is between 125 and 155 million years old, relatively young in geologic terms. One explanation of the formation of the Bay Area includes a great sub-glacial river flowing through Raccoon Straits, and pouring out over the soft rock between present Marin and San Francisco counties. According to Dr. Gordon Salisbury, a leading authority on Marin County and a noted geologist, the Sacramento River once flowed under a glacier, which covered the whole region, and fell in a water-fall over the Golden Gate. The whole bay area was covered by a mile-deep glacier and the Tiburon peninsula, a thousand to twelve hundred years ago, was at least 50 feet below sea level. The only area not covered by the glaciers was Point Reyes, where there is absolutely no sedimentary rock to be found but only rotten granite of igneous origin. The melting of the great glacier could have raised the sea level and worn down the Golden Gate, allowing' higher seas to rush in and make the bay as we know it. The shaley green rock which is so common in southern Marin is probably volcanic thrust. Quartz, feldspar, and mica are our common local rocks and minerals. Some, rocks found here are found in only a few other places in the world: the blue and lavender rocks which contain glaccophame are found only in Japan and the Italian Riviera, in a similar form. The green volcanic thrusts, the chlorites, are also fairly unusual. Near the eastern summit of Mt. Tamalpais there are numerous quartz veins said to contain gold. They have been worked, but are too poor to pay for the labor. Additional Comments: Extracted from: Shark Point - High Point An Illustrated History of TIBURON & BELVEDERE IN MARIN COUNTY, CALIFORNIA BY EIGHTH GRADERS OF THE REED SCHOOL CLASSES OF 1954, 1955, 1956, 1957, 1958 PUBLISHED BY THE REED SCHOOL DISTRICT PARENT-TEACHER CLUB BELVEDERE-TIBURON MCMLVIII Designed by Lawton Kennedy, San Francisco 3000 Copies Printed by R. G. Fontana & Son, San Anselmo File at: http://ftp.rootsweb.com/pub/usgenweb/ca/marin/history/1958/sharkpoi/glaciolo520nms.txt This file has been created by a form at http://www.genrecords.net/cafiles/ File size: 2.6 Kb