252 Forty- SIXTH Report oi>j the State Museum. ' 



When examined with the microscope the red brown blades seem to 

 be goethite. They are wholly without pleochroism and, under the micro- 

 scope, have the same red brown shade as the Lake Superior goethite, and 

 also have the parallel extinction of the rhombic forms. They resemble 

 in shape, size and distribution the actinolite described below from 

 other contact products. The rounded black ore grains are, at least in 

 part, magnetite, as the magnet abstracts fine grained ore from the 

 powder. Dark grains of black ore are inclosed within the goethite 

 blades. 



The colorless fresh ground is made up of interlaced plagioclase plates 

 which show few and interrupted twin lamellae. They present both the 

 albite and pericline systems of twinning, and are often marked by 

 undulose extinction. The maximum angle of extinction is 18° on a 

 side and the feldspar may be near labradorite. Crystals, where the 

 broad, twinning bands extinguish uniformly with sharp border, > adjoin 

 those where the undulose extinction completely blurs the outlines of 

 the separate bands, and this is in a wholly massive rock which shows 

 not the slightest trace of strong crushing, or of any force acting upon 

 it from without. 



The clear spaces are mostly aggregates of feldspar plates liLe those in 

 the general ground, with many rounded grains of black ore scattered in 

 irregular masses, but with traces of octahedral form, or blades having 

 exactly the same shape, size and distribution as the goethite blades, but 

 being now black and made up of a close set or congeries of minute 

 black grains. Here the goethite blades have probably been changed 

 to magnetite. Some of the clear spaces are made up of a mottled net- 

 work of indeterminate fibers, with a soft aggregate polarization, which 

 suggests a fine grained muscoAdte growth. The whole rock is a very 

 fresh and very curious goethite-magnetite-plagioclase contact rock. 



Specimen ]^o. 2, marked " Dyke," with which the above rock was in 

 contact, is a black basic eruptive rock like that at Thetford, Vt. The 

 phenocrysts of black basaltic hornblende, 2-4 mm. across, are as per- 

 fectly shaped, seen on the polished face, as those from Bohemia, and 

 larger ones, 10-15 mm. across, appear in the fractured surface of the 

 same rock. With a lens the large hornblendes at one end of the slide 

 are seen to be large perfect crystals, and to pass, toward the other 

 end, into more and more corroded forms, until at last only traces 

 remain, while a nearly colorless to greenish pyroxene, faintly brown 

 toward the border, appeared with about the same size as the hornblcLdes, 

 and increases in number of crystals as the hornblende disappears, and 

 incloses many unoriented fragments of the latter. The pyroxene is a 



