THE GEOLOGIC DAY 429 



But when it comes to minute comparison, they are by no means 

 exckisively to be trusted. If we find ourselves following along the 

 shore-line of an older, settling land-mass, and there are indications 

 that the land settled as a whole without tilting, or that, if it tilted, 

 we are still following one coeval shore-line, which was the farthest 

 extent of the overlap of the time, we may often be sure of a good 

 degree of contemporaneity, independent of fossils. Of course, if we 

 regard black shales as colored by pollen and spores, it may be said 

 that the black shale is a faunal characteristic. But if we disregard 

 the species and genera of spores, it becomes a mere physical char- 

 acteristic, dependent on climate, like a bed of salt. Then we may 

 fairly ask if the physical change which leads to the sudden appear- 

 ance of a bed of black shale above a limestone (like the Marcellus 

 above the Corniferous) is not likely to be closely contemporaneous 

 over a wide area. We may extend such illustrations indefinitely. 

 The point that I would make is that, while the paleontologist can 

 sometimes draw fine lines of time-division, a careful stratigrapher, 

 a paleogeographer, can at times draw equally valuable lines of time- 

 division, as nearly the same in different places, relatively to the lengths 

 of the intervals separated, as the divisions of civil time. 



If objection is made to using paleontology for the larger and 

 broader time-determinations, and using various other methods for 

 details, and not always drawing the line at the same place in 

 using terms applied to these divisions in the different regions, we 

 can again fall back on the analogy with the divisions of common 

 time, where the sun rules the year, and the moon long ruled the 

 month, while the finer and more exact divisions depend on other 

 data, and the year does not begin or end exactly at the same time 

 at every place. 



