GEOLOGY OF NORTH ATLANTIC GILLIGAN 219 



appear on all counts to have been either absent or to have formed 

 only a very small part of the area. Volcanic rocks of acid type, 

 such as the spherulitic felsites and feldspar porphyries, denote, no 

 doubt, surface and hypapyssal manifestations of the igneous activity 

 bringing the granites into position. Sedimentary rocks of grits, 

 sandstones, and chertly limestones were fairly common, and have 

 yielded numerous pebbles to the formations named above, as well 

 as much of the finer material. 



The mica-schist pebbles represent, no doubt, altered sedimentary 

 rocks. It is quite probable, then, that the succession on the ancient 

 land mass may have been: 



Top. Unaltered sedimentary rocks with volcanic rocks, mica 

 schists, quartz schists, and other altered sedimentary rocks. 

 Base. A complex of acid igneous rocks, mechanically de- 

 formed, invaded by granite masses and associated dykes of 

 pegmatites, feldspar porphyries, etc. 



Can we find in the Archean lands surrounding the North Atlantic 

 such rock types as are here indicated ? 



Europe. — In the portions which can now be examined in the ap- 

 propriate positions in the British Isles and Scandinavia the rock 

 types are such as could only yield a small part of the material, a real 

 test being the microcline, and, except for some pegmatite dykes such 

 as occur in the neighborhood of Cape Wrath, microcline is a compara- 

 tively rare mineral. 



Greenland. — Here on the east and west coasts Archean rocks occur, 

 mainly of granite with gray gneiss. The granite frequently contains 

 hornblende, and is traversed by intrusions of syenite and sodalite 

 syenite. 



There are also quartzites, clay slates, and limestones which are 

 correlated with the Heckla Hook system of Spitzbergen. We do not 

 find here again those types which would yield the granitic sediments. 

 Further, it has to be borne in mind that Silurian rocks covered much 

 of Greenland, and these were folded and contorted by movements 

 before the deposition of the red sandstone of Old Red Sandstone age. 

 The Archean of this region, then, could not apparently have yielded 

 much to the Devonian sandstone and later rocks unless, of course, 

 the unknown interior of Greenland contains rocks of the right type, 

 which were exposed in Old Red Sandstone and Carboniferous times. 



Labrador. — Coleman says that the northeastern part of Labrador 

 is very like the northwest of Scotland and parts of Scandinavia and 

 Finland in geology and physiography. 



Between the pre- Cambrian and the Pleistocene no formations are 

 known, and Coleman suggests that the area may have been dry land 



