206 THE CEYSTAL FALLS IRON BEARING DISTRICT. 



(lesniosites, and atlinoles.' The general characters of the minerals being the 

 same, I shall describe the structure whicli characterizes the rocks. 



SPII.OSITES. 



The ordinary- spilosites are distinctly mottled in hand specimens and 

 show clearly to the naked eye in thin section the oval spots which char- 

 acterize them. These oval areas are commonly 4 millimeters long, and in 

 rare cases even longer. They are frequently connected, forming chains. 

 Tlie spots are appreciably darker than the mass in which they lie, and are 

 composed of chlorite, quartz, feldspar, and rutile, Avith a small amount of 

 muscovite, the chlorite being the chief mineral. The surrounding mass 

 consists essentially of muscovite, -c^uartz, and feldspar, with rutile crystals 

 and flakes of hematite, and with a very slight amount of chlorite. The 

 different proportions of chlorite and muscovite seem to cause the difference 

 between the spots and the groundmass (lig. A, PI. XXXVII). In some of the 

 spilosites we find a few flakes of biotite and needles of actinolite; however, 

 these are always very subordinate in quantity to the chlorite. 



■ In the ordinary form described these spots consist essentially of bisili- 

 cates. Others also have been noted in which these spots are white and lie 

 in the fine-grained dark mass composing the greater part of the slides. 

 Thus far it seems only one instance of the occurrence of sucli a variety of 

 the spilosites has been described. This is by Van Werveke, to whose 

 description reference is made by ZirkeP and Rosenbusch.^ These white 

 spots are composed essentially of albite feldspar, with only a minor amount 

 of chlorite and epidote. The feldspar grains are much larger than those 

 which take part in the constitution of the mass surrounding the spots. 

 This mass is made up of quartz and feldspar, chlorite, epidote, and some 

 sphene, with sheaves of actinolite scattered through it, and in one section 

 clumps of biotite were observed mixed with the chlorite, though in very 

 subordinate quantity (figs. A and B, PI. XXXVI). 



'tjberden spilosit aiul desmosit Zinckon's, by Lossen: Zeitschr. Deiitsch. Geol. Geeell., Vol. 

 XXIV, 1872, p. 701. 



Durcli iliabas veriinderte Schiefer iui Gebiel der Saar and Musel, by Vau Werveke: Leoiuinl's 

 Jahrb., Vol. II, 1884, p. 225. 



An iuterestiug contact rock, with note on contact metauiorpbisni, by W. M. Hutchings: Geol. 

 Mag., Vol.11, pp. 122, 1G3. 



Numerous other references may be found in Chemische Geologie, by Koth, Bd. Ill, and iu petro- 

 .graphical works of Zirkel and Roseubu.sch. 



■^Zirkel, Pet.,Vol.II,p. 719. 



^Rosenbusch, Vol. II, 3d ed., p. 1177. 



