THE 
AMERICAN GEOLOGIST 
Vol. XII. DEC EMBER, 1893. No. <i. 
GEOLOGIC TIME; AS INDICATED BY THE SEDI- 
MENTARY ROCKS OF NORTH AMERICA. 
By Chari.es D. Walcott. Washington. D. C. 
COXTENTS. 
PAOK. 
1. Introduction 343 
2. (irowth of Continent 34fi 
:). Geographic Conditions 348 
1. Sediments Deposited in tin: Cordilleras Sea Mi) 
Mechanical Sediments 360 
Chemical Sediments 351 
( 'onditions of Deposition 351 
Rate of Deposit in Former Times 355 
5. Paleozoic Sediments of the Cordilleran Sea ::."i7 
ti. Duration of Paleozoic Time in the Cordilleran Area :i">9 
Estimates from Mechanical Sedimentation 359 
Estimates from Chemical Sedimentation :<61 
Rate of Deposition of recent cleposits 362 
Was Deposition of Chemical Sidiments more rapid in 
Paleozoic time.' 363 
Area of Deposition in Paleozoic time :(tf:'. 
Conditions favorable for Rapid Deposition of Carlwnate 
of Lime :{•'. I 
Kstimate from Deposition of Calcium, etc.. etc :W.". 
Time Ratios of Geologic Periods 306 
8. Duration of post-Archean Geologic Time :>'.7 
'.». Description of Map :tt>8 
Introduction. 
Of all subjects of speculative geology few areniore attractiveor more 
uncertain in positive results than geologic time. The physicists have 
drawn the lines closer and closer until the geologist is told that he must 
bring his estimates of the age of the earth within a limit of from ten to 
thirty millions of years. The geologist masses his observations and re- 
plies that more time is required, and suggests to the physicist that 
there may be an error somewhere in his data or the method of his treat- 
*Vice-Presidential address before Section E, A. A. \.S.. Madison. Wis., Vug. IT. 1893. 
