WEATHEEIXG m COLD AND WAEH CLIMATES 268 



Pumpelly, too, has shown^ that the diabase dike at Stamford, 

 Massachusetts, had undergone extensive decomposition prior 

 to the deposition of the Cambrian conglomerates. Of equal 

 interest and still greater economic importance was the sugges- 

 tion by this same authority, subsequently abundantly confirmed 

 by W. B. Potter,^ that beds of iron ore lying on the western 

 flank of Iron Mountain, Missouri, and covered by Silurian lime- 

 stones, were true detrital deposits resulting from the pre-Silurian 

 breaking down of the ore-bearing porphyry forming the mass 



— rrr? - 













^- W- 













■^ u 



" 'i'-Cjn " t* 



•;\ 









■^ 1 



'^v, ,_^ *- 



*• 











\ ■* tf 











Crairatc 



,\- '"- 













^ If 











• 



'->-*■ 











, 



^ 



. *- " ■'Vv 











t^ 















■* * •• Jkf 













•- -» -»|"^ 













- , '*. -S W tfa£"SMU70£L AtUWVK 











*- " ^^V*-% 













*' .- -vK 













^ -^\a^ 

























»*"'*•'• *^\Q£j 



^t/ai/wMf Itmerfyrti^^ui/sificti 









*v * ^\ .^^ 



rN-^ 











■* «7=*'-' 



** ' 1 











«- ' «< 



' * ^ -^ 













'^ ; ^ 











♦ * 



.•* .'' _^^T\ 



"V Siaf^Tttsfr- 



iirrtjufouet 



*. 



*^ * •- » « «■ 









•■ 4. T 



^\-Cfc«:>^ ZAKM Mt/Jioy \ 









^ , .' 





Sas*-^ /^ 









Cfw/niti' -^ 





^^^^^^s: 









* 





^^^^S 











'« *1 - 1 r* 



^t'^^§ 



Fig. 23. 



of the mountain. These and other' illustrations that might be 

 given point unmistakably to the identity of geological processes 

 and correspondence in results since the earliest times, even did 

 not analogy and the thousands of feet of secondary rocks furnish 

 us safe criteria upon which to base our inferences. 



(7) Eelative Rapidity of Weathering in Warm and Cold Cli- 

 mates. — For many years an impression has prevailed to the 

 effect that rocks decomposed more rapidly in warm and moist 

 than in cold climates. While, owing to abundance of vegeta- 

 tion and other supposed favorable conditions, a more rapid 



1 Ibid., YoL II, 1891, p. 209. 



2 Jour. U. S. Assoc. Charcoal Iron Workers, Vol. VI, p. 23. 



»See also T. Sterry Hunt, Tlie Decay of Eocks Geologically Considered, 

 Am. Jour, of Science, Vol. ZXVI, 1883, p. 190. 



