14 



BASIC AND ULTRABASIC IGNEOUS ROCKS— BENSON. [M ' M0,B ?^ I S^; 



In Rum, also (Harker '08) (Fig. 4) the Tertiary basalts have been invaded by plutonic 

 masses. The ultrabasic rocks occupy the highest position in the complex; their lower anothite- 

 bearing member (harrisite) is clearly the younger, and its junction with the overlying peridotite 

 is an intrusion-brecci. The eucrite-gabbro invades the ultrabasic rocks but lies for the most 



Fio. 3. — Geological map (somewhat simplified) and section of Skye. (After Harker.) 

 1. Torridonian sediments. 2. Cambrian limestone. 3. Mesozoic sediments. 4. Tertiary agglomerate. 

 5. Basalt with some dolerite-sills. 6. Peridotite. 7. Gabbro. 8. Granite. 9. Granophyre. 



u:$s°w. 



S.S5°E 



r 7 "' -j Peridotite 



AHivaliteO 



SkS/Sgi Harrisite 



ilV!il( 



Eucrite 

 Granite 



Fig. 4. — Geological section showing the relations of the plutonic rocks in Rum. (After Harker.) 



part beneath them. The junction between these two masses is a zone of fragmental peridotite 

 inclosed in veins of gabbro, which is sometimes a hundred yards in width. The granite in 

 turn invades the gabbro, but lies for the most part beneath it. In several regions their mutual 

 reaction has produced hybrid rocks, which solidified with a primary gneissis structure, owing 



