THE AKCH^AX FORMATION OF THE ABUKUMA PLATEAU. 221 



zonall y coii«ti'iicted zircon, red iiv^n-glance, opaque iron ore.s, and 

 Jastly, apatite, are the usual guests. A bluish schiller, so common 

 in the Swedish granites, is not observed. 



In tlie advanced stage of decomposition, the mineral resolves itself 

 into pseudophitic scales, w^hose tufts and aggregates are arranged 

 at right angles, and also parallel, to the c-axis. The epidoti- 

 zation seems here to ha\^e not taken place ; l)ut if it does occur amidst 

 the feldspar-substance, then the material for its formation must ha\e 

 been surely derived fr<^m the hornblende, evidence in favour of this 

 being easily deduced from the presence of ropy strings ol chloritic 

 matter directly connected witli the degenerating amphibole, and pene- 

 trated and inhltrated in the feldspar along the clefts in the latter. 

 The polarization -colour is languid and dull, ranging from yelloAvish- 

 brown to grey ; a prominent feature is, h(jwever, the presence of the 

 parallel-fibrous structure in crystals in a somewhat advanced stage 

 of decomposition. 



The niicroclliie is present only in small quantities. Macroscopicallv, 

 it can not be distinguished from orthoclase, as tlieir colours and lus- 

 tres are quite similar. I nder the microscope the microcline nature can 

 only be recognized bv its characteristic reticulated or cross-hatching 

 structure. The mi lierai is usually of a small, irregular form, filling 

 the interstices of other components, and also forming the outer z(jne of 

 the plagioclase or orth(j(jlase. It is generally fresh, and pellucid, and is 

 poor in liquid-inclusions ; consequently it can not be supposed to ha\e 

 been produced by the albitization of orthoclase, like that of granite in 

 Socotra.^ It Ijelongs to the latest generation. At times larger grains 

 seem to occur in the rock-mass, and these are partly changed 

 i]]to muscovite. Small microcline forms, too-ether with o-rains of 

 quartz, a. part of the njck, producing thereby what is called the 



1 A Sauer, Zeitschr. d. deutschen geol. Oeaellschaft, vol. XL. p. i4ü. 



