THE ARCHiEAX FORMATION OF THE ABUKUMA PLATEAU. 263 



devoid of externiil outlines. Masses of iron glance, both deep red 

 and opaque incxlilications, adhere to the crystals of the hornblende, and 

 also form local accuniiilations in them. This rock crops out at tlie dis- 

 trict-boundary of Kikuta and Higashi-Shirakawa, on the (lozaisho road, 

 being cut sharply by hornblende-granite, where tlie latter assumes 

 a more or less schistose structure (GHG, Profile C-1), Plate XX^'). 



h) Not far from the last locality, and directly overlying the pre- 

 ceding, we find a schist which is surely a modification of the rock 

 just described. It is a greenish, fine banded, imperfectly, fissile, feld- 

 spathose schist. witVi sericitic membranes and the tufts of a brownish 

 tourmaline on its cleaved surface. Under the microscope a bluish- 

 green, pleochroic hornblende assuming long, sheaf-like forms, is seen 

 in more or less parallel alignment, but Locally tlie crystids are thrown 

 indiscriminately together so as to form a more or less intricate felt- 

 work. The interstices between them are occupied by the fresh, clear 

 feldspar which is sharply bounded, polngonal, and well adjusted with the 

 neighhouring pohigons. These polygons are peppered through with 

 grains of black iron ore which, by reflected light, presents a bluish- 

 black lustre and lamellar structure. It is, therefore, iron glance, but 

 not magnetite, with which it is often confounded. The heart- and 

 knee-shaped twins of rutile are scattered through the section ; it must he 

 expresslij remarked that this mineral has hitherto not been observed, in the 

 allied rocks of the Takanuki series. This rock occurs associated with the 

 tourmaline-bearing mica schist, to be described in the sequel. 



c) Some of the rocks higher up in the series, associated with 

 schists such as that just described, are very similar in appearance to 

 common chlorite schist. Indeed they are compact, bluish-green, 

 rudely fissile, slaty rocks which, on cursory examination, might be 

 very often taken for chlorite schists. Examined under the microscope, 

 the predominating mineral, the hornblende, is seen to be present in 



