Johnson and Warren — Geology of Rhode Island. 25 



The rock is therefore perfemic, polmitic, permirlic, and 

 rnagnesiferous, its coordinates in the quantitative classification 

 being 5, 3, 1, 2. Furthermore it falls in section 5 of its order, 

 and in section 1 of its rang, and may therefore be further 

 defined as perolic and permiric. As there is as yet no name in 

 the quantitative classification for either the order or rang in 

 which this rock falls, it is necessary to choose a name. Rhodare* 

 and Rhodase (-ose) have been chosen, using the name of the 

 state in which the rock occurs for a stem to which the appro- 

 priate termination may be affixed. This has been chosen in 

 place of Cumberland — since the latter is the name of an obscure 

 and almost unknown town and might be confused with Cumber- 

 land, England, a well known locality. 



The rock finds a place in the classification in which there 

 are practically no heretofore adequately studied rocks and is 

 therefore of particular interest. 



As the olivine is the only one of the groundmass minerals 

 whose exact chemical composition has been determined directly, 

 it was assumed, in apportioning the FeO, MgO, and MnO 

 between the four modal minerals, olivine, magnetite, ilmenite, 

 and spinel, that the magnetite is represented by the formula 

 Fe n Fe 2 m 4 , the spinel by MgAl 2 4 , and that the remaining 

 MgO and the small amount of MnO are contained entirely in 

 the olivine and ilmenite. It seems unlikely, however, that any 

 considerable error is involved in this assumption. Adjusting, 

 therefore, the above mentioned oxides between the olivine and 

 the ilmenite in accordance with the ratios obtained from the 

 mineral of the olivine, we obtain the following as the true 

 composition, or mode, for the rock : 





M 



ode. 







Composition 



of the 



ilmenite 







Per cent. 



Per cent. 









by 



by volume 



Sp. gr. 



calculated to 100$. 



TVT"! T» PTfl 1 





WGitrlit 



to 100$. 

 0-8 









1X1. 1 11 C 1 (X 1 . 



Orthoclase 





0-56 



2-55 



TiO„ 



53-6 



Labradorite 











FeO 



42-5 



Ab 3 An 4 





9-23 



13-7 



2-69 



MnO 



1-3 



Olivine 











MgO 



2-6 



(hyalosidei 



•ite) 



46-08 



49-4 



3-73 









Magnetite 





20-65 



15-9 



5-17 





100-00 



Ilmenite 





18-63 



15-2 



5-0 







Spinel 





3-55 



3-9 



3.6 







Sulphides 





1-15 



1-1 



4-1 







99-85 



100-00 



analysis (less H 2 = 0'42 per cent). It does not affect dependent figures 

 materially and it has not been thought worth while to recalculate the whole 

 for so trifling a matter. 



* The use of the name Ehodare, etc. was first suggested by Professor L. 

 V. Pirsson, to whom the writer's thanks are due. 



