The paper deals with the Delmontian and upper Mohnian strata of the San Joaquin Valley, which are well known for their extreme lithological variations.

On the basis of lithological and paleontological studies of material obtained from 150 wells and several surface sections the whole column has been divided into a number of units representing definite time divisions. An attempt has been made to define the principal types of micro-faunal assemblages found in different parts of each unit, to appraise the ecological significance of these types and to survey their distribution in relation to lithological variations of the sediments of each unit.

The results of the study are illustrated by lantern slides showing: (1) lithological features and organic content of the recognized facies; (2) areal distribution of the facies; and (3) isopachous maps of the Delmontian and upper Mohnian beds.

(Presented with permission of the Geological Society of America.)

End_of_Article - Last_Page 1877------------