194 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



MgO 11.00 



CaO 10.24 



Na.O 2.89 



K.0 47 



MnO .=^4 



100.02 



The feldspar of the rock is much kaolinized and clouded in spots. 

 As a result of this, many tiny flakes of a highly doubly refracting 

 mineral are present. This mineral, sericite, often penetrates the 

 bounding planes between the hornblendes and frequently the larger 

 cracks in the latter mineral. This process of sericitization is pecu- 

 liar in that its effects are local, i. e., one section of a feldspar may be 

 completely changed, while the contiguous crystal may not have 

 suffered any alteration whatever. Albite twinning, sometimes 

 accompanied by pericline twinning, is frequent, though not the rule. 

 The small extinctions, symmetrical with respect to the traces of the 

 albite lamellae, indicate a feldspar of the andesine series. 



Occasionally there occurs as inclusions in the hornblende and in 

 the feldspar a fibrous mineral, evidently a member of the mica 

 group. Its exact nature, further than this, cannot be ascertained, 

 owing to the paucity of strong diagnostic features. It is yellow in 

 color, strongly dichroic, with rays vibrating parallel to the cleavage 

 planes of a yellow tint and colorless normal to this direction. The 

 hornblende, near at hand, has been bleached, and the yellowish-brown 

 color of the mineral in question naturally leads to the supposition 

 that part of the iron content of the hornblende has been appropriated. 

 It forms an intermediate link between the muscovite, which is 

 present in slight amount, and the bleached peripheral parts of the 

 hornblende. 



One other constituent deserves mention, i. e., magnetite present 

 as inclusions in both hornblende and feldspar. It is irregular in 

 shape and is frequently surrounded by a pale halo. 



NUGSUAKS PENINSULA 



Kaersiit. — Returning now to the mainland of Nugsuaks peninsula 

 at Kook and traveling west to Kaersut, the gneissoid crystallines 

 still continue overlain by. cretaceous shales and sandstones, inter- 

 calated with coaly streaks and basalt flows. At an altitude of 880 

 feet above the plant beds the shales have been baked and the lignite 

 converted to carbonite by the intrusion of a mass of horizontally 

 bedded peridotite which forms a cliff 200 feet high. 



