

GEOGRAPHICAL HISTORY OF DOLERITES. 281 



of Mull, and Gribun west of Mull, and east of the Treslmish Islands, 

 and opposite Lamlash in the Holy Island, east of Arran. 



In some continental localities trachylyte is spherulitic, as at 

 Bobenhausen, and it is perlitic at Marostica near Eassano. 1 



Geographical Distribution of Basalt. The large areas occupied 

 by basalt can only be adequately appreciated with the aid of a geo- 

 logical map. They occupy a great space in the southern Eifel ; there 

 is a larger district in the Westerwald, and immense spreads in the 

 Vogelsberg, the Rhon, Mittelgebirge, and other parts of northern 

 Bohemia. Smaller exhibitions are seen in the Oelberg, in Petersberg, 

 and the Nonnenstromberg in the Siebengebirge, at Unkel, at Scheids- 

 berg, near Remagen ; the Landskron, near Neuenahr ; Steinheim, near 

 Hanau ; Wenneberg in Ries, Kemnath in the Fichtelgebirge, Groditz- 

 berg and Striegau in Silesia, Suhl in the Thiiringerwald ; and many 

 places in Saxony, Bohemia, Moravia, Styria, Hungary, and Transyl- 

 vania. In North Italy basalts occur at Fonte del Capo, near Avesa ; 

 Vestena Nuova, south of Monte Bolca ; Radicofani, in Tuscany ; and 

 among the lavas of Etna. In the Auvergne, basalts are seen at Mont 

 Rognon, the Plateau of Cozent, the Plateau of Prudelles, the Puy de 

 Charade, Puy de Come, Puy de Coliere, and the lavas of Gravenoire. 

 There are a few localities for basalt in the extreme south of Sweden, 

 such as Sosdala and Hoor. Basalts are well known in Greenland, 

 at Ovifak in Iceland, the Faroe Isles, and Inner Hebrides ; at Paran- 

 agua in Venezuela, in the Galapagos Islands, in the Sandwich 

 Islands, north of Melbourne in Victoria, St. Helena, the Isle of 

 Reunion, at Funchal in Madeira, at Palma, and at Cruz in 

 Teneriffe. 



Types of Basalt in North. America. The basalts of the Fortieth 

 Parallel belong to two types. In the Elkhead region, and the 

 Kawsoh Mountains in Western Nevada, these rocks are nepheline- 

 basalt ; but in all other localities there is no trace of nepheline, 

 and the rocks are felspar basalts. The latter rock usually consists 

 of plagioclase, augite, and olivine ; but on the upper Snake River it 

 is composed of quartz, plagioclase, augite, and magnetite, without any 

 olivine, so that it makes a transition to the neighbouring augite-bear- 

 ing quartz trachyte ; but the ground mass is free from quartz. South 

 of the Yampa River, hauyine occurs as an inclusion in colourless 

 crystals of plagioclase. 



The nepheline basalt in the Elk Mountains is light grey and very 

 porous. In the fine ground mass the eye distinguishes augite and 

 olivine ; while the microscope shows biotite, magnetite, nepheline, 

 plagioclase. and gothite. A dyke called the Rampart, only six feet 

 wide, rises to a height of 30 to 60 feet, and extends for four or five 

 miles. It is formed of basaltic columns arranged horizontally. It is 



1 Hyalomelane was defined as distinguished from tachylyte, by not forming a 

 gelatinous-silica with acids. But Professor Judd and Mr. Grenville Cole give 

 strong reasons for rejecting the term. The rock occurs in Germany, at Ostheim 

 in the Witterau, and at Sahaburg in the Reinhardswald. A similar rock oc- 

 curs in the Ruby Valley range, in the Fortieth Parallel Region, U. S. A, 



