A HISTORY OF SCIENCE 



present knowledge. Mountains of this formation, as 

 the Adirondacks and the Storm King range, overlooking 

 the Hudson near West Point, are the patriarchs of their 

 kind, beside which Alleghanies and Sierra Nevadas are 

 recent upstarts, and Rockies, Alps, and Andes are mere 

 parvenus of yesterday. 



The Laurentian rocks were at first spoken of as repre- 

 senting "Azoic" time; but in 1846 Dawson found a 

 formation deep in their midst which was believed to be 

 the fossil relic of a very low form of life, and after that it 

 became customary to speak of the system as " Eozoic." 

 Still more recently the title of Dawson 's supposed fossil 

 to rank as such has been questioned, and Dana's sug- 

 gestion that the early rocks be termed merely Archaean 

 has met with general favor. Murchison and Sedg- 

 wick's Silurian, Devonian, and Carboniferous groups 

 (the ages of invertebrates, of fishes, and of coal plants, 

 respectively) are together spoken of as representing 

 Paleozoic time. William Smith's system of strata, 

 next above these, once called "secondary," represents 

 Mesozoic time, or the age of reptiles. Still higher, or 

 more recent, are Cuvier and Brongniart's tertiary rocks, 

 representing the age of mammals. Lastly, the most 

 recent formations, dating back, however, to a period 

 far enough from recent in any but a geological sense, 

 are classed as quaternary, representing the age of 

 man. 



It must not be supposed, however, that the successive 

 " ages" of the geologist are shut off from one another in 

 any such arbitrary way as this verbal classification 

 might seem to suggest. In point of fact, these " ages " 

 have no better warrant for existence than have the 



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