428 ALFRED C. LANE 



sissippian to that of the Pcnnsylvanian. The change may, of course, 

 have occupied considerable time in its spread, but probably only a 

 fraction of the duration of each period. Salt beds, whether formed 

 in desert wastes or inlets of the ocean, point to a dry climate. 



4. If one could only get samples of water in which the strata 

 were buried which had not changed in the meantime, one might, in 

 the case of open marine strata, be able to date them from the pro- 

 gressive change in the character of the sea water. This may be of 

 more value in the future than in the past, as it probably can be used 

 only on water carefully preserved from deep borings in slightly 

 disturbed synclinals where numerous beds are impervious. 



5. Changes in the elevation of the land, and consequently in 

 the shore-line, produce changes in the sedimentation in which climate 

 may co-operate. These changes in the sediment-determining factors 

 may be slow, like the tilting of the basin of the Great Lakes, now 

 going on. But even in such cases they may be nearly simultaneous 

 over long stretches of shore-line. They may also be sudden, like 

 the uplifts of the South American coast described by Darwin and 

 numerous other earthquake disturbances. In general, it may be 

 said to be likely that a sudden change, involving the injection of 

 fine mud in the ocean water, is not likely to be extremely local. 



As a result of these changes, the fauna is driven hither and 

 thither, and more or less modified by the stress of circumstance. 



If the difference in sedimentation slowly progresses, it is quite 

 possible that the corresponding change of fauna will be equally 

 slow in spreading from point to point. Thus, in determining what 

 is really genuinely coeval, there is often no reason to prefer the evi- 

 dence of fossils to that of sedimentation, if all the factors of the early 

 geography are duly taken into account. 



The great advantage that the fossils have is that they never come 

 back to their original combinations. The course of life has never 

 really gone backward, whereas sandstones, limestones, and shales 

 of recent times may be undistinguishable from those of earlier times. 

 Thus, when it comes to determining the general place in the geologi- 

 cal column, to deciding whether the Lake Superior sandstone was 

 "New Red," "Old Red" or coeval with the Cambrian, fossils, if 

 obtainable in sufficient quantity, far outclass other kinds of evidence. 



