HISTORY OF GEOLOGICAL. SURVEY. 37 



THE LABRADOR SYSTEM. 



The group of rocks referred by us to the Labrador system are first 

 described in the 1871 report, and certain passages in the history of its 

 exploration may be of considerable importance. The names of "Norian 

 system" and "Norite rocks" were applied to this group in the report after 

 a suggestion by Dr. Hunt. Upon reflection it seems more proper to use 

 the first name suggested for the system, rather than the lithological 

 appellation for a characteristic member. 



The first locality described is in Waterville. Its discovery was due to 

 the uncovering of the ledges by the remarkable rain-storm ending Oct. 4, 

 1 869. The ravages of the freshet were described by Prof. G. H. Perkins, 

 PH. D., of Burlington, Vt, who speaks of the ledge as a " black hornblendic 

 rock." In May, 1870, Mr. Huntington went up the same stream and 

 brought back specimens of the dark rock, which he thought might be 

 labradorite. He carried a fragment of it to Dr. T. Sterry Hunt, of 

 Montreal, for examination, March 21, 1871. Dr. Hunt wrote as follows 

 concerning this rock to Mr. Huntington : 



"The blue granular crystalline rock from Waterville, N. H., consists chiefly of a 

 feldspar allied to labradorite. I have not separated the grains to get them quite pure, 

 but the mass is seen under a glass to consist of the bluish-grey cleavable feldspar, with 

 some mica, probably biotite, and a little magnetic iron ore. From a pulverized sample 

 the magnet takes up about 5 per cent, of magnetic grains ; these contain a little titan- 

 ium. The analysis of the material thus freed from the magnetic portion gave me, 

 silica, 50.30; alumina, 25.10; protoxide of iron, 4.23; lime, 14.07; magnesia, 2.95; 

 volatile, 0.70 : loss (alkalies), 2.65100.00. I have found the feldspar of the so-called 

 labradorite or norite rocks very variable in composition, being sometimes more and 

 other times less basic than typical labradorite." "The analysis agrees closely with 

 what might be expected from an admixture of labradorite with biotite. It (the rock) 

 may hold a little hornblende, but I did not discern any. Thus the rock agrees chemi- 

 cally and mineralogically with much of the norite of the labradorite series of rocks, in 

 which titaniferous iron ore and biotite not unfrequently occur." 



About the same time the following passage was written by Dr. Hunt in 

 a letter to the state geologist. By oversight, the second passage was 

 printed in a communication to the American Journal of Science, January, 

 1872, instead of the first. The error was corrected in the report for 1871. 



