156 THE GEOLOGIST. 



the circumambient pasty rock, and, laminating, streaking, and con- 

 torting it in the "squeeze and jam" of its intermural expression, pro- 

 duced the ribboned-structured mica-schist and gneiss.* 



When we regard the extensive areas still exposed of the old gneiss 

 and similar-aged rocks in various parts of the world, and which pro- 

 bably have remained uncovered by any sedimentary deposit whatever 

 from the first hour that the golden sun tinged their brine-washed 

 crowns to the present play of his cheering rays upon their grey and 

 barren fronts, we may well ask if those oldest gneissic rocks have 

 thus been formed ? 



We must, however, look upon these granitoid and gneissic founda- 

 tions as the buttresses, denuded and weathered out in the lapse of 

 incomprehensible ages from the originally circumambient beds, and 

 exposed in this way to our view, rather than as dykes of molten 

 matter, forced completely through open fissures into the upper air. 

 We have alluded to the different ages of granite-formation and their 

 outbursts by the influence of internal heat on successive sedimentary 

 floors ; may we thence look to find any diff'erence of composition, 

 marking the difl'erence of the age in which each was generated and 

 irrupted 1 Mr. Sterry Hunt has done something towards this know- 

 ledge. He has pointed out that the oldest granite contains most 

 soda, and that the quantity of that alkali diminishes sensibly in the 

 several granitic masses in proportion to the proximity of their epoch 

 of formation to our times. Hence this proportional quantity of one 

 chemical ingredient may some day be made subservient to an approxi- 

 mate registration of geological time upon the great chronological dial. 

 As the first granites, or gneissic rocks, were worn down into sub- 

 marine sediments, to be afterwards changed in the progress of natural 

 phenomena into newer granites and metamorphic rocks, from those 

 sedimentary materials the primeval oceans dissolved out and accumu- 

 lated much of that soluble substance ; and so, those regenerated and 

 less alkaline granitoid rocks being again worn down, their sediments 

 were also in the lapse of time formed into newer granites and schists 

 with a still less quantity of alkaline matter. 



But let us go back to the old gneiss and the law of upheaval by 



• See Mr. Scrope's paper in The GEOLoaisT, vol. i. page 361. 



