J. J. Stevenson — Age of the Rocky Mountains. 



Iron sesquioxide 0*70 1 -02 



Manganese sesquioxide . .. 3-14 2-09 



Copper oxide 0-87) „. 6-82) 



Magneaia_., 22-50) ' 18-29) 



Water 9-90 1'92 9'30 1*88 



Moisture 1 8'80 10-32 



One half the water is driven off at a temperature of 100° Q, 

 and very little more is lost even up to. 200° C., and a full red 

 heat is required to expel the last traces. It is hence probable 

 that the moisture which goes off below 110° does not belong 

 to the mineral and should not be regarded in deducing the 

 formula. The formula obtain.. I is 2M.M >. :^i0 2 +2H,0, which 

 is identical with that of sepiolite, of which it is a new and inter- 

 esting variety. Its blowpipe characters, and its behavior with 

 acids are the same as those of sepiolite. It gelatinizes with 

 hydrochloric acid though not entirely decomposed. The green 

 variety, as shown in the analvsis above, contains considerable 

 copper, which is obviously the cause of the color, and which 

 seems to replace the magnesia in the composition of the 



Hamilton College, Feb. 14. 



Art. XXXVI.— On Dr. Peales Xot.es on the Age of the Rocky 

 Mountains in Colorado; by J. J. Stevenson, Professor of 

 Geology in the University of New York. 



" I have read Dr. Peale's notes with a good deal of care, but 

 his long discussion of my conclusions contains very little m 

 the way of direct a riri im Jut which seems to me to call for a 

 reply. At the same time it is necessary to correct some of Dr. 

 Peale's statements, which, no doubt without any such intention 

 on -bis part, certainly tend to give a false impression respecting 

 ' facts and my ] 



Th, 



hrd paragraph 



.« ^3 datTaTsufficient to extend his generaliza- 

 bons to the entio II.. -V M-- mi in Svstem, I. on the other 

 hand, feel no sin lata, which were 



Procured within a smaller area. The opening paragraph of 

 ^ap. xvii of Wheeler, vol. iii, contains a full statement of my 

 Pmion concerning the value of my data. 



