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University of California Publications in Geology [Vol. 9 



ference in attitude of the strata. From Mussel Rock north to the 

 landslide at Thornton Station the beds have an average dip to the 

 northeast of fifty or sixty degrees. The strike for this section varies 

 between north forty and north sixty degrees west. Beyond Thorton 

 Station the strike is nearly parallel to the cliff with a small east dip. 

 The sudden and marked change in the attitude of the strata at this 

 point commands more than the usual interest. The lithological char- 

 acter of the rocks appears not to be- greatly different in the two sec- 

 tions, but the suggested stratigraphic discordance, together with the 

 faunal break, which will be discussed on a following page, suggests 

 the possibility of an unconformity, and warrant separation of the 

 series into an upper and a lower horizon. 



The rocks of the Merced Series consist of fine-grained gray 

 sandstones and sandy shales, usually soft and friable, being little 

 more than compact sand. Occasionally thin, hard calcareous lay- 

 ers and thin lignitic layers are interstratified with the softer mate- 

 rial. In a few localities, near the base of the series, a small 

 amount of conglomerate was observed. With this exception the 

 sediments are principally fine-grained soft sandstone and clays. 



One of the most remarkable lithological features of the whole 

 series is the occurrence of a large area of shell agglomerate in 

 the higher portions of the hills one and one-quarter miles south 

 and a little west of Baden Station. The strata are composed 

 almost entirely of fragments of marine shells. Fine sand and 

 gravel compose the ground-mass in which the shell fragments are 

 embedded. This deposit marks an, old beach line or littoral zone 

 and is important in showing the shallow-water conditions which 

 existed during a part of Merced time. The total thickness of the 

 Merced Series, as measured by Professor Lawson, amounts to a 

 little more than one mile. 



The Merced Series is overlain, unconformably, by a belt of 

 nearly horizontal deposits which stretch entirely across the pen- 

 insula from the ocean beach to San Francisco Bay. These deposits 

 are composed principally of light-yellow and brown sands and 

 clays, with occasional seams of gravel and lignitic material near 

 the base. At least a part of these sediments were designated the 

 Terrace Formations by Professor Lawson in a publication to which 

 reference has previously been made. The term "Terrace Forma- 

 tions" as used in this publication may include more than was 

 originally included by Professor Lawson. Together with the allu- 



