Johnson and Warren — Geology of Rhode Island. 



chiefly in the replacement of the remaining olivine and actin- 

 olite with serpentine. 



The magnetite-ilmenite matrix seems to have been the part 

 of the rock least affected. 



For the purpose of checking in a general way the conclusions 

 reached through microscopic study as to the mineral and chem- 

 ical changes that have taken place in the rock, two partial chem- 

 ical analyses have been made, one of the " chloritic " type, and 

 the other of the "serpen time," the later showing very little 

 actinolite. A single specimen cannot of course be expected to 

 represent the exact altered product of a rock of the composition 

 of the representative sample taken for the original type, and an 

 extensive sampling of the altered types, had there been time 

 and opportunity to do it, would undoubtedly have yielded more 

 satisfactory results. Nevertheless the two analyses given in 

 the accompanying table, together with that of the unaltered 

 rock, serve to sustain the conclusions already reached, and are 

 instructive in showing the general character of the chemical 

 changes which have taken place. 



Unaltered *Chloritic Serpentine 

 type type type 



Sp. Gr 4-005-3*92 3-85-3-80 3-65-3-56 



Si0 2 22-35 20-89 19-98 



TiO t ._ --. 10-00 9-57 9-76 



A1 2 3 526 6-93 6-75 



Fe„O g --- 14-05 17-81 19-25 



FeO 28-84 26-04 21'42 



Fernet.... (32-26) (32'7l) (30'13) 



MnO .. -43 -40 



MgO 16-10 15-65 16-83 



CaO 1-17 -96 flost 



K„0 -10 none tr. 



N a o -44 tr. tr. 



HO -42 2-71 4-77 



99-26 



100-54 



99-32 



Comparing the three analyses we see that there has been com- 

 paratively little material actually removed from the rock during 

 the extensive alteration process. The alkalies, some lime and 

 silica, have been removed, and also some of the iron in the ser- 

 pentine type. The iron has suffered some oxidation. The 

 alumina seems to have increased relatively, and its presence 



*This analysis was made by Mr. J. W. Shaw, formerly assistant in the 

 department of Geology. 



f The amount of lime ppt. was very small indeed. 



Am. Jotjr. Sci. — Fourth Series, Vol. XXV, No. 145 — January, 1908. 

 3 



