Age of the Earth. 377 



assumption made in plotting the sedimentary thicknesses is 

 that these, inter se, are roughly comparable as regards the 

 times of accumulation. As I have already pointed out, this 

 seems probable save in the case of the earlier pre-Cambrian 

 sediments, which we might expect would have been accu- 

 mulated more locally. The thicknesses of the several strata 

 1 have laid out according to the data collected by Sollas. 

 The radioactive times are plotted above the points on the 

 base-line to which their geological positions assign them. 

 We have from the lead ratios two early- Algonkian results 

 and two post-Jatulian results. The Archaean results by 

 helium and lead cannot be located on the base-line save 

 by the indications of the other results. 



If there was accord between the stratigraphical column 

 and the radioactive data, the latter should be ranged on 

 straight lines which necessarily pass through the origin 

 (present time). We find them, however, ranged upon 

 curves. I have plotted the age of the ocean as determined 

 by solvent denudation; erecting for this purpose an ordinate 

 of 150 millions of years at the beginning of Algonkian time. 

 The curves for helium and lead flow into this line in recent 

 periods. 



If now we assume that the time indications of the lead ratios 

 are correct, we are presented with the following alternatives 

 as regards the amendment of the sedimentary column. 



We assume that the stratigraphical column for post- 

 Carboniferous time is in actuality much as we have plotted 

 it, and draw a right line from the origin through the 

 three results for the age of Carboniferous, Devonian, and 

 Silurian-Ordovician periods, as derived from the lead ratio. 

 This is equivalent to assuming that the error in the strati- 

 graphical record, is to be sought mainly in the pre-Cambrian 

 records. We therefore plot the early Algonkian and post- 

 Jatulian results on this line. We have now to make the 

 following amendment on the recorded thicknesses of the 

 pre-Cambrian sediments. Algonkian sediments rise from 

 82,000 feet to 381,000 and 441,000 feet, according to which 

 of the two early- Algonkian results we select. Keweenawan 

 sediments rise from 50,000 feet to 245,000 or 359,000 feet 

 according as we select among the two Jatulian results. 



While it is true that important unconformities exist in 

 the pre-Cambrian succession, the sedimentation equivalents of 

 which are not found as yet, it seems incredible that amounts 

 of: sediments nearly double the entire thickness of post- 

 Algonkian rocks and from 70 to 80 miles in cumulative 

 depth, can have escaped investigation. There is another 



