102 



University of California Publications. 



[Geology 



INTRODUCTION. 



In the following paper an attempt has been made to bring 

 together the already ascertained facts concerning the Palaeon- 

 tology of the Martinez Group, and to add to them a considerable 

 body of new evidence. The present investigation was begun by 

 Professor J. C. Merriam, who made an extensive collection of 

 Chico, Martinez and Tejon fossils from several localities in 

 Contra Costa County, to the south and west of the town of Mar- 

 tinez. These formations were mapped by Professor Merriam in 

 detail, the stratigraphic relationships were determined, and many 

 new elements were recognized in the faunas. The completion of 

 this work was suggested to the writer by Professor Merriam. The 

 continuation of the investigation has consisted in an examination 

 of all the known Martinez outcrops in the State, in the collection 

 of additional fossils, in the study of the fauna with special con- 

 sideration of correlation, and in the description of a number of 

 new and characteristic forms. 



During the early months of 1904, about four weeks of field 

 work were devoted to a study of the geologic and stratigraphic 

 relations of these formations in the vicinity of Benicia, Aran 

 Point and Martinez. Later in the year two trips were made to 

 Lake County, where fossils of Martinez age were reported to 

 occur. During the summer of 1904 about nine weeks were spent 

 in mapping the Napa quadrangle, upon which are located the 

 regions about Martinez and Benicia. In connection with this 

 work an attempt was made to discover any stratigraphic relation- 

 ships which might exist between the Martinez beds of Lake 

 County and those in the vicinity of Karquines Strait. The 

 study of the fauna has resulted in the description of twenty-one 

 new species. 



HISTORICAL REVIEW. 



The Martinez formation was first recognized in 1869 by Wil- 

 iiam M. Gabb* in volume two of his work on the Palaeontology 

 of California. In the earlier volume! on the Palaeontology of 

 California Gabb divided his Cretaceous into an upper and lower 



*Eop. Geol. Surv. of Calif. Palaeontology, Vol. II, p. 13 op. preface. 

 tEep. Geol. Surv. of Calif. Palaeontology, Vol. I, 1864. 



