April 18, 1906. At 5:12 in the morning San Francisco was rocked by a powerful earthquake. The magnitude was 7.8 or 7.9 and the death toll is estimated today at about 3,000 people.
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They call these source beds “hot shales” because they also tend to have concentrations of radioactive elements, which make them easy to recognize on well logs, which are basically measurements of information taken down a drill hole. One tool measures gamma-ray intensity, which is greater in radioactive materials. Similar rocks of similar age are found in North Africa as well – Algeria, Libya, and Egypt have such shales and oil explorationists are really only just beginning to understand them.
The known oil from Silurian source rocks in Arabia and Algeria amounts to probably about 95% of the Silurian-sourced oil in the world, but there’s some oil in Silurian rocks in the U.S. as well. We’ll get to that in a few days.
—Richard I. Gibson
Role of glaciation