TERTIARY TIMES. 



ORIGIN OF THE TEEM TERTIARY LOWER, MIDDLE, AND UPPER, OR 

 EOCENE, MIOCENE, AND PLIOCENE TERTIARIES THEIR MINERAL 

 COMPOSITION AND SUCCESSION DIFFERENT IN DIFFERENT BASINS 

 OR AREAS OF DEPOSIT FLORA AND FAUNA OF THE RESPECTIVE 

 SUBDIVISIONS PHYSICAL CONDITIONS UNDER WHICH THESE GREW 

 AND WERE DEPOSITED GIGANTIC AND . INTERMEDIATE FORMS OF 

 EOCENE MAMMALS APPROXIMATION TO EXISTING DISTRIBUTIONS 

 IN MIOCENE AND PLIOCENE TIMES ECONOMIC PRODUCTS OF THE 

 SYSTEM. 



WHEN the earlier geologists arranged the stratified rocks of 

 the earth-crust into Primary, Secondary, and Tertiary, they 

 closed the Secondary with the Chalk, and regarded as Ter- 

 tiary all the sediments that occur above that formation. In 

 their estimation Tertiary strata were comparatively limited, 

 and they had no conception of the extent, thickness, and 

 variety of sediments, or of the long periods which this 

 thickness and variety of deposits must necessarily imply. 

 To them primary was equivalent to universal ; secondary- 

 was still very extensive, though not universal ; but the ter- 

 tiaries were mere local patches occupying shallow depres- 

 sions in the older formations. As research went forward, 

 however, modern geologists began to discover that tertiary 

 strata differed widely among themselves both in composi- 

 tion and fossil contents, and that as a whole they were 

 entitled to be ranked in schemes of classification as a system 

 of sedimentary deposits. It was also found that while all 



