4O PHYSICAL GEOGRAPHY. 



The oxygen ratio of the bases and silica afforded is nearly i :i, and of the iron 

 and magnesia about i :2 ; whence the formula (JFe-|-iMg) 2 S. This is then a chryso- 

 lite, containing an unusually large per centage of iron (here a constituent of the min- 

 eral, and not owing to the presence of impurities) . The amount of iron is not strange, 

 considering the fact that the rock contains, diffused throughout it, so much free iron ore. 



This chrysolite has the same ratio deduced for hyalosiderite, but still differs widely 

 in fusibility and other characters. It is, in fact, a true chrysolite in all respects, while 

 hyalosiderite is a doubtful compound, probably owing its fusibility in part to the potash 

 present. B. B. the chrysolite is nearly infusible. 



The following is Mr. Dana's analysis of another specimen of labradorite : 



This feldspar has a grayish-white color, is destitute of iridescence, and only care- 

 ful searching reveals any striations. Two analyses afforded, 



I. II. III. Mean. 



SiO 2 52.15 52.36 52.25 



A1 2 O 8 27.63 27.39 27.51 



Fe 2 O 8 1.09 1.07 i. 08 



MgO .92 i .06 .... .99 



CaO 13-10 13-45 13-22 



NaO 3.68 3.68 



KO .... 2.18 2.18 



100.91 



Both analyses show that the labradorite of this region is remarkable for the large 

 proportion of lime present. 



The next point in the history of these rocks in New Hampshire relates 

 to a discussion respecting the discovery of the mineral aggregate named 

 "ossipyte." In a letter of May i, 1872 (which, with Prof. Dana's, is pub- 

 lished in full in the report for 1871), Dr. Hunt speaks thus concerning 

 Mr. E. S. Dana's paper: "He remarks that a rock consisting of labra- 

 dor with chrysolite (olivine) has not been previously described. It was, 

 however, long since noticed by Macculloch in Skye, and by G. Rose at 

 Elfdalen. \Senft die Felsarten ; also, Geology of Canada, p. 650.]" 



The substance of this note having been communicated to Mr. Dana, 

 the following letter came from his father : 



PROF. C. H. HITCHCOCK. 



My Dear Sir In the absence of my son, Mr. Edward S. Dana, now on his way to 

 Europe, I write a brief reply to your letter of the 2gth inst. You stated that Prof. T. 

 Sterry Hunt, in a recent note, objects to Mr. Dana's remark that a rock of the compo- 

 sition of the ossipyte of Waterville had not before been described, and that he refers 

 to Macculloch as having observed the same in Skye, and G. Rose another example of 

 it at Elfdalen in Sweden. Mr. Hunt is evidently unaware of the facts. Macculloch 



