324 Palmer — Notes on the Andes of N. W. Argentina. 



The red sandstone seems to have been deposited in a tan- 

 gential manner as regards time. That is the deposits are not 

 contemporaneous, but vary in age from place to place. Thus 

 Stelzner speaks of Phsetic psam mites in the Salta and Jnjuy 

 region ; Professor Bowman has found Cretaceous fossils at 

 Fongo Mainique, Peru (Lat. 11° S.) ; and the fossils in the 

 red sandstone of the Calchaqui region indicate Lower Jurassic. 

 Though fossils are entirely wanting in this red sandstone forma- 

 tion throughout the whole eastern border of the mountains in 

 Bolivia for a distance of seven hundred miles and are very 

 rare in Argentina, the present expedition found a fossiliferous 

 horizon at La Poma. Professor Schuchert was so kind as to 

 study these and has tentatively identified Cerithinella 

 armatum and a Cerithium (species ?), which are gastropods, 

 suggestive of Lower Jurassic age. The collections of fossils 

 included only the two species. Professor Schuchert also sub- 

 mitted the fossils to Dr. Stanton, who seemed to think that 

 similar species had been identified by Moriche in the Jurassic 

 of Chile, and that he would expect to find them in the Jurassic 

 of Argentina. Dr. Stanton further said : " I should hesitate to 

 say positively that these fossils are Middle Jurassic, or even 

 that they are Jurassic, on the basis of their unsupported 

 evidence. There are so many forms of similar appearance at 

 various horizons in the Mesozoic and Cenozoic that I should 

 consider it unsafe to make a definite determination of age on 

 such forms alone, unless I could be absolutely sure of a 

 specific determination." 



At the point where the fossils were found, a little south of 

 La Poma and close to the river, a section of about 20 meters 

 was measured. As this section is at the center of a large 

 anticline, it is the base or near the base of the formation. The 

 section is as follows, from the top down : 



An indefinite thickness (1,000 meters or more) of red sandstone, 

 shale, and conglomerate. 



30 cm — micaceous sand, or soft sandstone. 

 180 cm — a heavy, single bed of sandstone. 



250 cm — sandstones and shales. The sandstone is in beds aver- 

 aging eight centimeters in thickness and is prominently 

 cross-bedded. 

 125 cm — variegated shales ; green, purple, and yellow. 

 210 cm — soft, fine-grained yellow sandstone, in beds of 1 to 5 

 centimeters. 

 60 cm — variegated shales. 



60 cm — fine-grained, yellow to brown and gray sandstone. 

 Alternating layers are hard and soft, some approaching 

 quartzites. 



