Palmer — Notes on the Andes of N . W. Argentina. 323 



forming the bottom of the valley. The relation of these folds 

 to the marginal faults is discussed later. 



The schists and quartzites on either side of the valley are of 

 great age and have been subjected to many crustal disturb- 

 ances. As a result the original structures have been completely 

 obliterated, and no statement can be made of the amount or 

 kinds of mashing and dislocation that they have suffered. 



The Ages of the Formations. 



As to the ages of the formations of this region but little can 

 be said. Stelzner is quoted in the Argentine " Agricultural 

 and Stock Census' 1 of 1909 as follows : — " The sandstone in 



Fig. 



Fig. 6. Sketch section of the Calchaqui Valley, looking north from La 

 Poma, showing a broad anticline on the west and a broad syncline on the 

 east. 



the provinces of Salta and Jujuy, of the Upper Cambrian 

 formation, rests on the Archean, and on this is found the lime- 

 stone and dolomite of Mendoza and San Juan and the sediments 

 of the Lower Silurian. Thereupon follows a break in the con- 

 tinuity to the Rhsetian. It includes a portion of sandstone 



and red psammite remarkable for its lack of fossils. Through 

 the more recent researches of Bodenbender we know that on 

 the Silurian limestones of the Jachal there are regular layers 

 of schist and psammite, which perhaps, represent the Upper 

 Silurian. Fossils have not yet been found. The latter form 

 a bed of gravel, psammite, and limestone with Devonian 

 fauna, which is being studied . . . by Dr. Kayser." 



Dr. Rudolph Martin,* a mining engineer of Salta, Argentina, 

 has found trilobites in the quartzite near Salta, which prove 

 that these metamorphosed sediments are of Paleozoic age. 

 Wolff, Raimondi, Phillipi, Steinmann, and many other writers 

 mention Silurian and Devonian rocks and fossils from many 

 places on the eastern margin of the Cordilleras. 



* Oral communication. 



