1914] Dickerson: Fauna of the Martinez Eocene of California 79 



(5) Gray-green shales, 250-300 feet. 



(4) Gray-green glauconitic sandstone, 50 feet. 



(3) Fine-grained, hard, gray sandstone, 200 feet. 



(2) Shales and argillaceous sandstones, 100 feet. 



(1) A brown, conglomeritic, basal sandstone, 50 to 100 feet in thickness. 



On the south side of the mountain the limestone, ten feet in thick- 

 ness, is interbedded with shales and fine gray micaceous sandstone. 

 From this evidence we conclude that: 



1. An unconformity exists between the Tejon and beds evidently 

 of Martinez age southwest of Mount Diablo, as well as between the 

 Tejon and Chico. 



2. This unconformity is marked by mollusc borings recognized in 

 localities six miles apart, and an angular unconformity is recognizable 

 in several places between the Tejon and the underlying Chico. 



Field relations show that the unconformity between the Tejon and 

 Martinez represents a time interval so long that at least several 

 hundred feet of thickness of Martinez were removed before the land 

 was lowered to receive the sediments of the Tejon sea directly upon 

 the Chico, the former basement of the Martinez. 



TYPE LOCALITY OF THE MARTINEZ 



STEATIGEAPHY 



Dr. Weaver 20 described the stratigraphy at the type locality as 

 follows : 



In the vicinity of the Strait of Carquinez the Chico, Martinez, Tejon and 

 Monterey have all participated in the folding of the strata, which has resulted 

 in the formation of a synclinal trough, the axis of which has a northwest to 

 southeast trend. The apex is situated about four miles to the north of Benicia. 

 The maximum width of this syncline, extending from a short distance west of 

 Pacheco on the east to Del Hambre Canon on the west, is about four miles. 

 In this cross-section the Chieo, Martinez, Tejon and Monterey are found in 

 succession toward the center of the syncline. The same holds true on the 

 northern side of the straits, except that the Monterey is not represented. To 

 the south and west of Martinez, on the western limb of the syncline, all of 

 these beds dip at high angles to the northeast. West of the syncline the Martinez 

 becomes thinner, and is represented by a narrow strip extending up nearly to 

 the head of Del Hambre Canon. At this locality the Martinez, together with 

 the Chico, dips to the southwest. 



20 Weaver, C. E., Contribution to the Palaeontology of the Martinez Group, 

 Univ. Calif. Publ. Bull. Dept. Geol., vol. 4, no. 5, p. 105, 1905. 



