22 BASIC AND ULTKABASIC IGNEOUS ROCKS— BENSON. 



Carboniferous or Permian conglomerate lies over a series of probably Devonian phyllites, in 

 which is a zone of porphyroid rocks consisting of sodic keratophyres and submarine flows of 

 diabase and tuffs. The whole series was invaded by gabbros apparently of lower Carboniferous 

 age. The whole has been much disturbed and sheared into flakes by the later Mesozoic folding 

 (Woldrich '12, '13). 



The latest basic intrusive rocks in north central Europe are the essexitic rocks of the Rh6n, 

 Vogelsberg and Lausitz, with which must be grouped the great masses of essexites, theralites, 

 teschenites, and picrites of the Bohemian Mittelgebirge. These form the typical Atlantic 

 or alkaline rocks of Becke ('03), formed during the fracture and differential movement of 

 blocks unfolded since Permian times. (See also Hibsch '03.) 



Of special interest, however, are the eruptions of very basic alkaline rocks, often melilite- 

 basalts in the south of the block-faulted Bavarian tableland. They occur in volcanic pipes 

 filled either by massive melilite-basalt, alnoite, etc., or by breccias including kimberlitic rocks 

 (Branca, '94, Schwartz, '05). 



NORTHERN FRANCE AND THE CHANNEL ISLANDS. 



Excepting the basic rocks of the Pyrenees and Alps, treated in the next chapter, there are 

 few masses of basic intrusive rock in France. A few small masses of serpentine and gabbro 

 have been noted in the folded Lower Paleozoic rocks of Brittany (Brun '05) , but no data are 

 available concerning the conditions of intrusion of these, nor of the gabbro of Pallet described 

 by Lacroix ('99), which invades a series of mica-schists with very poorly exposed boundaries. 

 The Iiercynian intrusions are probably represented in the Channel Islands by the hornblende- 

 gabbro and diorite of Guernsey described by Parkinson ('07). 



