POSTGLACIAL OXIDATION 293 



between the condition at tlie surface and at anj' depth if the deposit is the 

 result of one and the same action. Even if there he a terminal moraine which 

 has taken a million years to form, and the ice front has never moved from 

 one spot for that time, and the lower portion he rotten while the top is fresh, 

 if we suppose an advance of a mile, we will have whatever is carried onward 

 mixed up in the carriage and deposited with a generally uniform appearance 

 at top and hottom. We conclude, therefore, that when a deposit shows a 

 similar state of £>xidation at top and hottom it is not soil rotting in place, and 

 if it shows no signs of stratification it is not sedimentary unless the condi- 

 tions of sedimentation were identical during the period covered by the whole 

 of the deposit. The presence of glaciated stones will, however, settle the 

 matter. 



"On the other hand, if a glacial deposit, which at the beginning showed the 

 above characteristic of uuiformitj'. lies for ages, say one thousand years, under 

 the influence of weather, frost, rain, etcetera, we can readily see that the sur- 

 face must begin to show a weathering distinct from that which was shown at 

 all depths by the weathered portion of the original deposit, and this weather- 

 ing in place will extend to varying depths according to the openness and 

 porosity of the mass; but in every case there never will be a uniformity of 

 weathering between the top and bottom layers of the mass. 



"We have, therefore, an infallible criterion for gauging the age of a glacial 

 deposit. There will be three conditions : 



"First. There will be a deposit which has been formed by the long continued 

 action of a glacier forming a moraine at a given line of advance. Here the 

 lower part of the deposit is the most oxidized and the fresh and recent ma- 

 terial is on the top. 



"Second. There has been the formation of a terminal moraine by an advance 

 followed by a continuous retreat. Here the criteria will be of two kinds: 



"a. It is an old moraine and the surface is more oxidized than the base, or 



"&., It is a comparatively receiit moraine and there is a uniformity of oxida- 

 tion from top to bottom. 



"From the latter we see that whether the contents be fresh or completely 

 rotten, the recency is shown by the uniformity of oxidization throughout, so 

 that there may be a recent moraine of entirely rotten and oxidized material if 

 the material was taken from a rotten surface, as well as a recent moraine of 

 perfectly fresh material taken from a well glaciated surface. Again, if we 

 find at all levels freshly rolled material mixed with perfectly rotted and oxi- 

 dized soil the formation is recent. 



"We can deduce the general rule: 



"Absolute uniformity in characteristics of a deposit of glaciated material 

 at all levels on a vertical section shows recency of formation, and it is innna- 

 terial whether the deposit consist of entirely fresh, entirely oxidized, or mixed 

 fresh and oxidized material." 



These various observations certainly nullify the evidence usually ad- 

 duced to prove an enormous lapse of time since the culmination of the 

 Glacial period, and support the earlier conclusions of Dana, Hitchcock, 

 Upham, and others, that the upper and lower till are quite distinct in 



