The Tertiary of Soutltern Lotver California. 531 



As a result of the writer's expedition, several preliminary papers 

 Lave been published.^ 



General Structure. 

 Orographically and geologically, the southern part of the Lower 

 Calif ornian Peninsula is divided into three distinctly different 

 regions (Fig. 1) : — 



(1) The Cape Range or Sierra de la Victoria, which forms the 

 mountainous southernmost extremity of the Peninsula, from Cape 

 San Lucas to La Paz, with a direction from south to north. It 

 is chiefly formed by old acid crystalline rocks : granite, syenite, 

 porphyry, quartz-porphyry ; also dioritic rocks in places (San 

 Antonio), with many metamorphic rocks like ortho- and paragneiss, 

 mica-schists, and marbles (Todos Santos), amphibolite (San 

 Antonio). They contain rich gold and silver veins at El Triunfo 

 and San Antonio. A region of younger Tertiary sandstones has 

 been found at the mouth of Santiago Valley on the Gulf coast 

 (indicated with points in Fig. 1). 



(2) The Magdalena Banqe (black in Fig. 1). This mountain 

 range, which rises from the Pacific Ocean, has been partly submerged. 

 Only the ruins of it are left. Actually, it has again entered a stage 

 of emersioii. Beginning in the south, it is represented by the 

 bare mountainous islands of Santa Margarita, Magdalena, and San 

 Lucas Mountain. Farther north it is represented again by the 

 Sierra Pintada or Sierra Santa Clara, which forms the Pacific coast 

 from Punta Abrojos (Lat. 26° 40') to Cape San Eugenio, and 

 terminates at Cedros Island. The distance from Santa Margarita 

 to Cedros Island is 600 kilometres. 



The rocks seem to be chiefly basic : diorite, amphibolite, and 

 chloritic schists. No granite was encountered. Mesozoic and 

 Tertiary intrusions of basic rocks were found on Santa Margarita 

 and Cedros Islands. White marbles and gray, hard sandstone 

 of great thickness, intensely folded, occur on Santa Margarita 

 Island. No fossils were found. The sandstones are pierced by 

 green rocks, which are partly much metamorphosed and contain 

 hornblende, biotite, and chlorite. 



(3) The Mesas or Central region extends from one side of the 

 Peninsula to the other, gradually rising from the Pacific coast 



^ Am. Heim, " Sur la geologie de la partie meridionale de la Basse Californie," 

 Comptes rendus Ac. d. Sc. Paris, t. 161, p. 419, 4th October, 1915. H. Douville, 

 " Les Orbitoides de la presqu'ile de Californie," Comptes rendus Ac. d. Sc. 

 Paris, t. 161, p. 409, 4tli October, 1915. Am. Heim, " Reisen im siidlichen 

 Teil der Halbinsel Niederkalifornien " (4 pi.), Zeitschrift der Ges. f. Erkunde, 

 Berlin, 1916. Am. Heim, " Charakterpflanzen der Halbinsel Niederkalifornien" 

 (12 pi.), in Vegetationsbilder v. Karsten & Schenlc, Jena, 1916. Ad. Hartmann, 

 " Wasseruntersuchungen im Gebiete der Magdalena Bay in Niederkalifornien " 

 (2 pL), Vierteljahrsschrift d. Nat. Ges. Zurich, 1919. Ad. Hartmann, " Ein 

 Beitrag zur Kolonisationsfrage des Westens von Nordamerika," Mitt. Aarg. 

 Nat. Ges., Aarau, 1919. Am. Heim, " Vulkane in der Umgebung der Oase La 

 Purisima auf der Halbinsel Niederkalifornien" (1 map, 3 pi., 7 fig.), Zeitschr. 

 fiir Vulkanologie, herausgeg. v. Imm. Friedldnder, Bd. vi, 1921. 



