FARABEE— SOUTH AMERICAN PETROGLYPHS 



these mountains and all the Indians are well acquainted with them; 

 but no one knows anything of the petroglyphs. From the negative 

 evidence of the present peoples we must conclude that the glyphs are 

 older than the immediate ancestors of the Indians. It may be 

 objected that the present tribes have recently immigrated to these 

 regions and could not be expected to have any knowledge of them, 

 yet similar things are found in every part of the country. 



The petroglyphs themselves give the best evidence of their age. 

 In protected places, where they occur on overhanging rocks, the 

 grooves exceed a quarter of an inch in depth, and it may be inferred 

 that they were of the same depth on the upper exposed surfaces 

 where the work was less difficult. The grooves were rubbed smooth 

 and hence would erode less rapidly than the other rock surface. In 

 some places the grooves have been further protected by deposits of 

 oxide of iron. The grooves have remained smoother than the rock 

 surface, making it possible to trace them by touch when they can- 

 not be seen. This would prove that the rock has eroded to the depth 

 of a quarter of an inch since the glyphs were made. While we can have 

 no definite idea of the rate of erosion, not knowing all the conditions 

 of climate, we know that granite decomposes very slowly and that 

 it would require a very long time to erode to this depth — certainly so 

 many generations that we should not expect any traditions of the 

 makers of the glyphs to survive. 



There has been a great deal of theorizing about the use and signifi- 

 cance of petroglyphs. They have been thought to be everything from 

 mere pastime occupations to serious historic records. The following 

 is a list of the more plausible uses suggested: Marks to indicate fords, 

 portages, and trails; fishing places; records of visits by individuals or 

 tribes; records of personal encounters; tribal marks, totems, resorts, 

 or boundaries; migration routes; astronomical purposes; records of 

 myths; religious symbols. Many have attempted to interpret them 

 by the use of known symbols used in other localities. This is a dan- 

 gerous method, because they may not have symbolic significance at 

 all, and, even if they have, the observed similarity is mere coinci- 

 dence. It is highly improbable that they are the product of idle 

 moments. The nature of primitive man would not lead him to spend 

 his leisure in such difficult, painstaking, and continued labor. He 

 could pass the time by doing absolutely nothing. Some of them may 

 be at fording places, where the river can be crossed by passing from 

 one rock to another when it would be impossible to cross in any other 

 way without a canoe. In the same way they may mark the ends of 

 trails which follow the line of outcrop across the lowlands. The out- 



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