This picture of a quarry among the diatom hills of California indicates to the imagination better than figures the countless myriads of the microscopic plants which were 
deposited in this place. The number has been calculated as represented by the numeral 1 with thirty ciphers attached. But for all we know, forty ciphers may be be equally 
correct. These diatoms, chiefly species of the genus Coscinodiscus, were developed in the locality where they are now found when this was a sheltered bay among an archi- 
pelago of islands, formed by the nascent peaks of the California coast. Among other peculiarities of the deposits is their exudation of petroleum, a phenomenon as yet not 
wholly explained, although probably connected with the fact that each diatom when alive contains a minute droplet of oil. 
XI 
A MIOCENE CATASTROPHE 
