170 i. 11. TVMUNSON 



most of the green spots in Rod Hods, is so small that it could easily 

 be effaced or removed. A tiny fragment of vegetable fiber or the 

 remains of a tow minute organisms of any kind probably would 

 suffice. 



Cause of gray and green bands in red beds: Barrett's hypothesis. — 

 Harroll" statos that in the Catskill formation of eastern Penn- 

 sylvania gray and green colors are typical of sandstones, and red 

 oolors of shales. Ho therefore suggests a causal relation between 

 coarseness oi grain and condition of the iron content, as follows: 



rhese relations show that then- was a tendency toward deoxidation during 

 the formation of the hods of sand, of oxidation during the deposition of the 

 Catskill muds. Where the clay and iron oxide were sparing in quantity, the 

 deoxidation was effective. The conditions which accompanied the deposition 

 of clay and iron oxide also permitted oxidation to dominate over deoxidation. 3 



The lack of oxidation of the iron in the sandstones, in spite of its lesser 

 quantity, suggests that more abundant ground-waters in the sands may have 

 kept out the air and permitted the organic matter to accomplish its effects, or 

 perhaps that here the ratio of organic matter was in excess of the ferric oxide. 1 



A few rare carbonaceous streaks have been observed in the Catskill and 

 the plant impressions are in places found in deoxidized shales. Coaly and 

 pyritiferous plant fossils are also preserved in some of the olive sandstones.-' 



No actual remnants of organic matter are reported to have been 

 found in red strata, though markings interpreted by Harroll as 

 rootlot marks are noted by him in certain horizons of rod shales. 



That physical Conditions of deposition alone should have favored 

 oxidation in the finer-grained sediments and retarded it in the 

 coarser seems highly improbablo. Where meteoric water moves 

 most freely, there the most oxygon is oarriod in solution. The more 

 rapid the circulation of ground-waters, the more effective are those 

 waters as oxidizing agents, instead of vice versa, as suggested by 

 Barrell. 



For the lesser quantity of iron in the sandstones wo already 

 have offered an explanatory hypothesis (p. 164). Tho smaller the 

 amount of ferric oxide present in a sediment, tho smaller, of course, 

 is the amount of organic matter necessary to bring about its reduc- 

 tion or the reduction of a sufficient part oi it to mask the oolor of 

 tho remainder. If organic matter wore distributed equally among 



l Op.cit. -•//»/(/.. i>. 45S. •'//»/</.. p. 400. •»//'/(/. 



