Authors Abstracts. 



ABSTRACT OF PAPER READ AT THE MONTREAL MEET- 

 ING OF THE GEOLOGICAL SOCIETY OF AMERICA. 



Weathering of Alnoite in Manheim, N. Y. By. C. H. Smyth, Jr. 



A somewhat altered dike of alnoite, consisting of biotite, serpentine, 

 magnetite, perofskite, apatite, and some calcite, is exposed on the east 

 bank of the East Canada Creek. Melilite, abundant in two neighbor- 

 ing dikes, is not apparent, doubtless being obscured by alteration. 



On the west bank the dike is weathered to a fine yellowish-brown 

 sandy clay, exposed about fifteen feet vertically. Under the micro- 

 scope, the weathered material is seen to consist chiefly of biotite, mag- 

 netite, and perofskite, the other minerals being no longer recog- 

 nizable. 



From chemical analysis, it is evident that the rock in weathering 

 has lost about 27 per cent., chiefly silica and magnesia, with less lime 

 and potash. Alumina and titanic oxide show a relative gain in the 

 same ratio, and are assumed to have remained constant. Iron also 

 shows a relative gain, but slightly less than that of alumina, while it 

 has undergone much oxidation. The amount of water has been very 

 largely increased. 



The greatest percentage of loss for a single constituent (excepting 

 C0 2 , which has totally disappeared) is shown in the case of potash, of 

 which 92.27 per cent, has been removed. Soda has lost about 75 

 per cent., magnesia, 49 per cent., lime 45 per cent., silica, 27 per cent., 

 and iron oxide less than 4 per cent. 



The process of weathering has involved this considerable solution, 

 together with oxidation and hydration. The accompanying physical 

 changes are a complete change of color, and a disintegration so thor- 

 ough that the material may be easily scooped out with the hands. 



The contrast between alteration and weathering is pronounced. 

 The" former led to the formation of serpentine and calcite, without 



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