DISTRIBUTION OF ARCH^AN ROCKS 359 



intense dynamic metamorphism to which they have been subjected, 

 in their extremely complex arrangement and in their laminated 

 and crushed condition. The Archaean, as thus defined, contains no 

 sandstone, conglomerate, limestone, or any other rock of undoubted 

 sedimentary origin, nor any considerable mass of quartz schist, 

 marble, or graphite schist. The rocks thus referred to the Archaean 

 are not necessarily all of the same age, but they are all of vast 

 antiquity and older than any other known series. They are of very 

 great but unknown thickness, for the bottom of them is nowhere 

 to be seen, and even when thrown up into mountain ranges, ero- 

 sion has in no case cut so deeply into these rocks as to expose 

 anything different below them. 



The reason for uniting these rocks into one group is not merely 

 their likeness in composition, which is not a sufficient criterion, 

 but because of their unique and uniformly complex structure, 

 their resemblance to one another and difference from any other 

 group of rocks, and their invariably fundamental position. 



The Distribution of the Archaean Rocks can at present be 

 stated only with much reserve, for they often grade into crystal- 

 line schists of demonstrably later date, and much that once was 

 referred to the Archaean is now known to be far more recent. 

 To accurately determine the distribution of the basal complex 

 will require the most extensive, minute, and laborious investiga- 

 tion. The northern part of North America, from the Arctic 

 Ocean to the Great Lakes, is made up of an immense area of 

 schistose rocks, estimated at more than 2,000,000 square miles in 

 extent. Over this vast region occur numerous areas of Archaean 

 rocks, but it is not yet possible to say how much of it belongs in 

 that group and how much is newer. 



Beside this principal region are several other minor ones. A 

 narrow band of schistose rocks extends, with some interruptions, 

 from Vermont to Georgia, with shorter parallel belts in eastern 

 Canada and New England. Another great axis is on the site of 

 the Rocky Mountain chain, with several shorter and generally 

 parallel belts from Mexico to Alaska. Isolated areas occur in 

 Missouri, central Texas, New Mexico, and Arizona. In all of 



