534 Arnold Helm — 



undetermined, the method of the U.S. Geological Survey is followed 

 in giving preliminary formational names according to localities. 

 The following seven names are proposed : Tepetate (indicated on 

 figures with T), Purisima nueva (P), Monterey (M), Isidro (I), 

 Comondii (C), Cuesta (Cu), Salada (S). 



Tepetate Formation". 



In the region east of Santa Margarita Island the unfolded Salada 

 Formation is unconformably underlain by a gently folded formation 

 of soft greenish sandstone, hard, well-stratified gray sandstone, 

 and greenish to violet clav several thousand feet in thickness 

 (Fig. 2). At the ranch El Tepetate (Lat. 24° 23', Long. 111° 8', see 

 T in Fig. 1) the beds of a soft greenish sandstone cross the bed of 

 the Arroyo Colorado with a dip of 4° towards the north-east. They 

 contain millions of a small Orbitoides with a central button. 

 Professor H. Douville, of Paris, kindly determined them as 

 Orthophragmina Pratti, Mich.,^ and thus considers the age of the 

 Tepetate Formation as Upper Eocene. Besides this species, 

 Douville mentions from El Tepetate Amphistegina Niasi Verbeek 

 (sub Nummulites), a species known from the Tongrian of the 

 Philippines, which, however, is not of much value for the determina- 

 tion of age. 



Following the dr}^ bed of the Arroyo Colorado from a place three 

 kilometres south-west of the Ranch El Tepetate towards the north- 

 east, the following section was noted, according to the gentle 

 north-easterly dip of the formatio^;i, upwards : — 



1. At the north end of Llano del Judillo well-stratified gray 

 sandstone weathering into hard plates with tracks of animals 

 on the rough surface. 



2. Violet and greenish clay, about 20 m. 



3. Greenish shaly sandstone, about 10 m. 



4. Compact soft greenish to white sandstone with black mica 

 and many Orthophragmina Pratti, 20 m. (?) 



5. Greenish shaly sandstone without Orthophragmina, about 

 10 m. 



6. "Well-stratified sandstone filled with Orthophragmina Pratti, 

 about 7 m. 



7. Greenish, well-stratified, shaly sandstone, about 7 m. 

 From El Tepetate the Orthojjhragmina sandstones were followed 



to the Oasis San Hilario, a distance of sixteen kilometres, where they 

 are overlain by Quaternary conglomerates and sandstones. Farther 

 toward the interior of the Peninsula, the greenish Tepetate Formation 

 is directly overlain with a slight unconformity by the brown sand- 

 stone of the central table mountains, which apparently belongs 

 to the Comondii Formation. 



On the horse traili from El Tepetate, four kilometres west of San 



^ Cf. Sch]umberger,\B.-S.(?. France, 4me serie, t. iii, p. 275, fig. A, and 

 pi. viii, figs. 2-3. 



