HANDBOOK FOR THE DEPARTMENT OF GEOLOGY. 



585 



Silica 



Alumina , 



Iron sesquioxide 

 Iron protoxide.. 



Magnesia 



Lime 



Soda 



Potash 



Water 



II. 



Per cl. 

 47.44 



Per ct. 

 43.09 



23.71 



17.45 



6.83 



18.99 



3.53 





1.95 



4.63 



C.47 



9.70 



0.40 



5.02 



3.34 



1.81 



1.73 



0.33 



Structure. — The rocks of this group are as a rule porpbyritic with a 

 holo-crystalliue groundmass, though sometimes there is present a small 

 amount of amorphous interstitial matter or base ; at times amygdal- 

 oidal. 



Colors. — The colors are dark, some shade of gray or brownish. 



Classification and nomenclature. — According to their varying mineral 

 composition Rosenbusch divides them into : 



Leucite teplirite = Leucite, augite, plagioclase rocks. 



Leucite basauite= Leucite, augite, plagioclase and olivine rocks. 



Nepheline teplirite=Nepbeline, plagioclase rocks. 



Neplieline basanite = Nepheline, plagioclase and olivino rocks. . 



The rocks it will be observed stand intermediate between the true 

 basalts and the nephelinites to be noted later. The distribution of 

 these rocks i», so far as now known, quite limited. 



The following localities and varieties are represented : 



Leucite tephriie : Tovalato, near Rome, Italy, 35752. 



Leucite basanite : Bosco Reale, Vesuvius, flow of 1751, 3654*2 ; II Granatello, Vesuvius, 

 flow of 1631, 36544; La Scala, Vesuvius, flow of 1631, 36547 ; Uncino, Vesuvius, 

 flow of 1760, 36545 ; Cisterna, Monte Somraa, 38738 and 38789 ; Vesuvius flow of 

 1855, 36546 ; do., flow of 1872, 36144; Vesuvius, 35724. 



Nepheline tephrite : Kleine Priessen, Bohemia, 36534 and 36535; Kostal, Bohemia, 

 36536; Calvarienberg, Poppenhausen, Rhon Mountains, 36532, 70227, and 70228; 

 Langenscheid, Nassau, Germany, 36537; Niedermendig, Prussia (with Hauyn), 

 34686; Tavolato, Rome, Italy, 36539; Rocco Monfina, Rome, Italy, 36540; Serra 

 de Tingua, Brazil, 70255. 



Nepheline basanite : Hundkoph, Salzungen, Germany, 70229; Stallberg, Rhon Moun- 

 tains, Germany, 70230; near Rossdorf, Germany, 70231 and 70238: near Weiler, 

 Baden, 35S59 ; Lobau, Saxony, 73116, 73117, and 73118. 



11. The picrite porphyrites. 



Under this head is placed, by Professor Rosenbusch, a small group 

 of rocks so far as now known, very limited in their distribution, and 

 which are regarded as the effusive forms of the plutonic picrites, as bear- 

 ing the same relation to these rocks as do the melaphyrs to the olivine 

 diabases. The essential constituents are therefore olivine and augite 

 with accessory apatite, iron ores and other minerals mentioned as oc- 

 curring in the true picrites. Structurally they differ from these rocks 



