Palmer — Notes on the Andes of N. W. Argentina. 315 



but locally it is red, green, blue, and brown. The texture 

 approaches the phyllitic, as there is not enough mica or coarse 

 quartz to make it highly schistose. Some of it is very badly 

 shattered, apparently by stresses in different directions applied 

 at different times, which developed a strong, slaty cleavage in 

 one, two or three directions. The high degree of this fissility 

 is marked by the difficulty of neatly trimming a specimen. 

 The constituents are in general so fine-grained that they are 

 not distinguishable under the hand-lens. The rocks of this 

 formation seem to be of sedimentary origin, as it is possible in 

 some outcrops to trace the former bedding by the bands of 

 quartzite now present. They have suffered so much compres- 

 sion that most of the original structure has been destroyed, 

 though some outcrops show closed folds of five or ten meter 

 radius, with many minor plications superposed on them. 



The source of the materials forming these " metasediments," 

 as it has been suggested we should call metamorphic rocks of 

 sedimentary origin, is a problem that has yet to be solved, and 

 which has, in fact, hardly been attacked. There is here a vast 

 amount of material. Outcrops of this schist and quartzite 

 formation occur more or less continuously over wide areas, and 

 the original sediments must have been from one to three kilo- 

 meters thick. These rocks form the major portion of the 

 Eastern Cordillera for many hundreds of kilometers. Among 

 the hypotheses as to the source of the materials are the follow- 

 ing: 



(1) That they were derived from a mountain area in what 

 is now the Pampas region. 



(2) That they were derived from an older system of moun- 

 tains in the general region of the present-day Maritime Cor- 

 dillera and Coast Ranges. 



(3) *That they were derived from a land mass lying west of 

 the present west coast of South America and which has now 

 completely slumped in. In this case there would be two pos- 

 sibilities; first, that the sediments were geosynclinal, or second, 

 that they were deposited on the edge of and just outside the 

 then continental shelf. Such marginal deposits are known to 

 be forming at the present day, but have not been recognized 

 in the sedimentary record. This hypothesis would accord well 

 with the idea that the Galapagos and other Pacific islands were 

 formerly connected to South America. 



Unfortunately no data were obtained which would tend to 

 prove or disprove any of these hypotheses. 



An interesting structural relation between the Paleozoic 

 metasediments and the Mesozoic sediments is shown in the 

 Calchaqui Valley. Though more fully discussed in Part II, 



* Suggested by Professor Joseph Barrell in a personal communication. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 226.— October, 1914. 

 22 



