32 Johnson and Warren — Geology of Rhode Island. 



3B will serve to give some idea of the relations of the different 

 minerals. 



Professor Wadsworth has noted the occurrence of talc and 

 dolomite as extreme alteration products of the rock. These 

 minerals seem, however, to be exceptional and are certainly 

 not characteristic of the alteration as now exposed. 



Conclusions regarding the alteration process. — The profound 

 alteration which has taken place in the rhodose appears to 

 have been affected by the long-continued action of waters from 

 the surface. It is most severe in the peripheral portions of 

 the rock mass and its progress seems to have been gradually 

 inward from the margins. 



The first change effected in the rock was the destruction of 

 the plagioclase and of the olivine and ore immediately adjoining. 

 The first product formed in the place of the feldspar is of 

 uncertain composition, but very readily changes into chlorite 

 and actinolite ; at least these two minerals appear almost imme- 

 diately. The chlorite can derive its aluminium only from the 

 feldspar, its magnesium from the olivine / its iron may and 

 undoubtedly does come from both the olivine and the ore. The 

 lime from the plagioclase goes to form actinolite whose other 

 bases seem to come principally from the olivine since it is the 

 olivine that is replaced by the actinolite. The alkalies and a 

 part of the lime have been removed. The titanium has either 

 remained in the form of ilmenite or else has passed into the 

 composition of the chlorite. It is perhaps remarkable that 

 rutile* or other oxides of titanium are characteristically absent 

 from all of the altered types. 



That the solutions carrying the alumina, lime and soda and 

 other products were diffused very generally through the rock 

 is proved by the bands of chlorite almost everywhere developed 

 between the ore and the olivine, as well as by the presence of 

 actinolite distributed through the rock. The veins carrying 

 actinolite, chlorite and hortonolite also bear evidence that 

 material was being actively transported. That these solutions 

 should deposit a mineral belonging to a group of minerals so 

 characteristic of igneous origin is of especial interest. 



The greater abundance of actinolite in certain portions of the 

 hill may be accounted for by supposing that the feldspar was 

 there more abundant and the supply of material for secondary 

 minerals therefore more abundant. On the other hand, it is 

 supposable that the actinolitic portions represent merely places 

 where the mineralizing solutions were for some reason more 

 abundant. 



After the series of reactions which gave rise to the chlorite 

 and actinolite were completed, further alteration resulted 



* In one or two instances reddish, grains associated with the ore have been 

 noted which may be rutile. 



