12 



GEOLOGICAL MEMOIRS. 



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Beyond the lines b b, b b the orthoklase is less developed, be- 

 comes mixed with about as much oligoklase and quartz, and then 

 forms a graphic granite, which at other parts, by the addition of 

 mica in small plates, puts on the appearance of ordinary granite. 



Orthite, Zircon, Malakon ?, Oerstadite ?, Apatite, Yttrotitanite, 

 Magnetite, &c., M^ere found here. 



The finest representation 

 given of the structure of such 

 granitic masses is shown in 

 the vertical section of the 

 felspar quarry at Helle near 

 N9eskilen(fig.5). The scale 

 may be judged of from the 

 section itself, which at the 

 highest point is about 1 5 feet. 

 The felspar is here quarried 

 for technical purposes. 



On the surface is seen a 

 covering of gneiss, not more 

 than from 1 to 2 feet thick, 

 showing a regular and nearly 

 perpendicular foliation ; be- 

 low this we have on the one 

 hand (a) orthoklase graphic 

 granite, and on the other 

 (b) oligoklase graphic gra- 

 nite. 



Still lower, the constituent 

 minerals of the granite, viz. 

 quartz {?'), orthoklase (o), 

 and mica (x), are developed 

 on an immense scale ; the 

 mica, even, being in plates 

 of enormous size and of 

 many square yards area. 

 The masses of quartz and 

 orthoklase here found some- 

 times show traces of cry- 

 stalline faces. 



Underneath the whole we 

 have graphic granite (m), 

 going over to ordinary gra- 

 nite of a fine grain. 



Several minerals occur 

 here, and amongst others may be mentioned two new minerals calle d 

 Alvite and Bragite, as well as Orthite in crystals and masses up to 

 the size of 14 to 15 lbs. 



From the observations made in various parts of this district it 

 would appear that the mica present in such granite has a very de- 

 terminate relation to the occurrence of extraneous minerals, which 



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