34 0. W. Hawes — Iron in Doleryies from New Hampshire. 



magnetic constituents withdrawn by passing a magnet over the 

 ic iron which may be present in the rock 

 can be recognized by treating this magnetic portion with an 

 acid solution of sulphate of copper and then examining it with 

 the microscope to see if any metallic copper is precipitated. If 

 metallic iron is present it exchanges places with the copper, and 

 crystalline aggregates of metallic copper, easily recognizable by 

 their color and luster, will be seen. But as" Dr. Andrews re- 

 marked in speaking of the Ovifak iron, in his inaugural address 

 before the British Association last summer, it has never been 

 found possible to detect with the microscope this iron which 

 was known to be present. It is proposed here to point out the 

 mode of occurrence of visible grains of metallic iron in dole- 

 rytes from New Hampshire. 

 * Upon the Dry river, a small stre 

 from Mount Washington, there ; 

 chrysolitic doleryte, which cut through the old ~ 

 rocks. These dolerytes are composed of labradorite, pyroxene, 

 chrysolite and magnetite, with a little mica ; and, though they 

 contain such decomposable materials, the rocks are remarkably 

 fresh, and all the minerals are clear when looked at in thin 

 sections with the microscope, showing no signs of alteration. 

 This may be due in part to the remarkable compactness of the 

 rock, and perhaps more to the great freshets in the spring time, 

 which remove any soft or loose material. 



Considering that the circumstances wotdd be favorable for 

 the preservation of metallic iron in these rocks if anv were 

 originally present, I tested for it according to the method be- 

 fore described, and the strength of the reaction was surprising. 

 The magnetic constituents treated with sulphate of copper ex- 

 hibited numerous bright crystalline aggregations of copper 

 which were plainly visible to the naked eye. The reaction 

 was so much more marked than any that I had obtained in 

 testing the trap rocks of the Connecticut valley, which con- 

 tain iron when not altered by decomposition, that I examined 

 the sections to ascertain if it could not be seen under the 

 microscope; and I found on shutting off the light from the 

 mirror below and examining them with light reflected only 

 from the section, that a few of the grains of magnetite possessed 

 a bright metallic center, which had the luster of metallic iron. 

 and which was very marked in the bluish-black magnetite. 

 Taking an unmounted section which possessed one of these 

 grains near its center, I treated it with sulphate of copper, 

 when the grain was covered with a coat of copper, proving it 

 to be iron. The following figure is drawn from a section of 

 the rock, and represents it as r : .. diameters. 



The black mineral is magnetite, and the light colored spot in 



