GEOLOGY AND SCENERY OF NORTHEAST COAST 99 



of feet. It is, indeed, possible that their fissures reached 

 quite to the surface and built volcanic cones and lava 

 plains long since destroyed. That inference is supported 

 by the discovery on the Labrador of just such volcanic 

 accumulations, although these have not yet been suffi- 

 ciently studied to show actual connection between the 

 lavas and the dikes of trap. That the latter were thrust 

 into the fissures of the mountain-core with enough energy 

 to force the molten rock to the surface is implied in the 

 conditions of Figure 14. 



Striped Island gets its name from a remarkable group of 

 thin, nearly horizontal sheets of black trap cutting common 

 gray gneiss. The causes of the intrusion here may have 

 differed from what they were in the case of the vertical 

 dikes, which, as we have seen, entered the base of the moun- 

 tain-range by a kind of permission ; great mountain blocks 

 moved apart and permitted the plastic trap to enter the 

 opening fissure. But the sheets of Striped Island, as they 

 forced their way into place, had apparently to lift a rock- 

 cover weighing countless millions of tons. Their intrusion 

 began along so-called " joints"; that is, microscopic though 

 continuous cracks previously developed' in the gneiss. 

 The imagination may well be staggered in the attempt 

 to grasp the magnitude of a force which could so thrust 

 fluid rock into almost infinitesimal cracks, wedging up a 

 whole mountain in the process as if a Titan had worked 

 with an omnipotent jack-screw; yet there seems to be no 

 escape from the conclusion that such a wonderful display 

 of power in the molten under-earth has taken place. 



In summary, then, the different formations composing 

 the Basement Complex of Labrador, though understood 



