126 



JOURNAL OF THE 

 PEGMATITE, OR GRAPHIC GRANITE. 



[April, 



Fig. 1 — Section parallel to laminae. Fig. 2.— Section transverse to laminae. 



" Feldspar, quartz, and mica are usually considered as the min- 

 erals essential to granite, the feldspar being most abundant in 

 quantity, and the proportion of quartz exceeding that of mica. 

 These minerals are united in what is termed a confused crystalli- 

 zation ; that is to say, there is no regular arrangement of the 

 crystals in granite, as in gneiss, except in the variety termed 

 graphic granite, which occurs mostly in granitic veins. This 

 variety is a compound of feldspar and quartz, so arranged as to 

 produce an imperfect laminar structure. The crystals of feld- 

 spar appear to have been first formed, leaving between them the 

 space now occupied by the darker colored quartz. This mine- 

 ral, when a section is made at right angles to the alternate 

 plates of feldspar and quartz, presents broken lines, which have 

 been compared to Hebrew characters." 



4. Section of Wacke, from Bujio Quarry, Panama R. R. 

 Section of Gravel ; ^ 



Section of Gravel ; 

 Section of Gravel, metamorphic ; 



Nos. 4, 5, 6 and 7 exhibited by P. H. Dudley. 



8. Slides of Heads of Hemiptera, including mouth-parts : ex- 

 hibited by L. RiEDERER. 



9. A slide of Diatoms from Rembang Bay, 31 generae, 319 

 forms, obtained from washings of coral : exhibited by E. A. 



SCHULTZE. 



10. A slide of Diatoms from Santa Monica, 348 forms : ex- 

 hibited by E. A. ScHULTZE. 



11. A slide of Diatoms from the Lystran Deposit, Siberia: 

 exhibited by E. A. Schultze. 



5- 

 6. 



7- 



From Chagres River, 

 at Gorgona. 



