NEW GEOLOGIC TIME TABLE 



601 



Association for the Advancement of Science). It will be seen that much 

 more time has been allowed the Cambrian and Ordovician than is usually 

 assigned them ; together they are allotted 43 per cent of the Paleozoic era. 

 The per cent of time for each period is stated throughout, but it should 

 be noted that these are rough estimates and not calculations based on the 

 known thickness of the formations composing the periods or systems. 

 The great length of Triassic time is based on the long and nearly com- 

 plete Mediterranean record. 



The horizontal lines or ordinates numbered 1 to 8 on the chart each 

 represent one" million square miles of the North American continent. 

 The two other horizontal lines give the areas for the "United States" and 

 "North America" as explained above; hence the extent of the inunda- 

 tions illustrated by the curves may be seen at a glance in relation to 

 present conditions. 



A detailed analysis of these curves shows that there have been 17 lows, 

 or inundations, separated from one another by as many highs, or emer- 

 gent periods. Of these, 11 are Paleozoic, 4 Mesozoic, and 2 Tertiary. 

 For easy reference, these are arranged in the following table, the amount 

 of area submerged being given in square miles, with the percentage. The 

 names in italics represent the marked submergences, 10 of which reach 

 over 20 per cent. 



Table of North American Inundations 



Present land area of North America, about 

 8,200,000 square miles. 



Present land area of North America between 



30° and fto° north latitude, about 



3,530,000 square miles. 



Time of greatest inun- 

 dations. 



In square 

 miles. 



In per 

 cent. 



Time of greatest inun- 

 dations. 



In square 

 miles. 



In per 

 cent. 



Middle Georgic 



Middle Acadic 



1,451,000 

 2,587,000 

 1,775,000 

 1,663,000 

 4,676,000 

 3,340.000 

 2,940.000 

 2,881,000 

 2,644,000 

 620,000 

 2,270,000 

 1,261,000 

 1,130,000 

 1,559,000 

 2,778,000 

 236,000 

 360,000 



17.6 

 31.6 

 21.7 

 22 7 

 57.2 

 40.0 

 35.9 

 35.2 

 20.1 

 7.6 

 27.7 

 15.4 

 13.8 

 19.0 

 33.9 

 2.9 

 4.4 



Middle Georgic 



Middle Acadic 



Middle Ozarkic 



Beekmantown 



Early Trenton 



Late Richmond 



Louisville 



Hamilton. 



421.000 



1,648.000 



1,016.000 



1,065,000 



2,158,000 



1,560,000 



1,246,000 



1,126,000 



874,000 



348 000 



1,283,000 



292,000 



646,000 



433,000 



1,354,000 



154,000 



234,000 



12.0 

 46.7 



Middle Ozarkic 



Beekmantown 



Early Trenton 



Late Richmond 



Louisville 



28 9 

 30.3 

 61.2 

 44.3 

 35.7 



Hamilton 



32.0 



Burlinqton 



Burlington 



Saint Louis 



24.8 



Saint Louis. 



10.0 



Late PottsvilUan 



Late Triassic 



Late PottsvilUan 



Late Triassic 



Late Jurassic 



Fredericksburg 



Niobrara ( estimated) . 

 Early Oligocene .... 

 Upper Miocene 



36.4 



8.4 



Late Jurassic 



18.4 



Fredericksburg 



Niobrara (estimated).. 



Early Oligocene 



Upper Miocene 



12.4 



41.3 



4.5 



6.7 



LI — Bull. Geol. Soc. Am., Vol. 20, 1908 



