Contortion and Metamorphism. 45 



Subsequent research has shown that this theory will 

 not hold ; for this, among other reasons, that we now 

 know gneissic rocks of almost all ages in the geological 

 scale. Thus in Scotland the gneissic rocks are of 

 Laurentian and Silurian age ; in Devon and Cornwall 

 we have gneiss both of so-called Devonian and Carboni- 

 ferous ages. In the Andes there are gneissic rocks of 

 the age of the Chalk, and in the Alps of the New Eed, 

 Liassic, Oolitic, and Cretaceous series; and in 1862 I 

 saw in the Alps an imperfect gneiss of Eocene date 

 pierced by granite veins, these strata being of the age 

 of some of the soft and often almost horizontal strata of 

 the London and Hampshire basins. It is therefore now 

 perfectly well known to geologists that the term Pri- 

 mitive, as applied to gneiss, is no longer tenable ; 

 and the old theory has been abandoned. 



I have stated that regions occupied by meta- 

 morphic rocks are apt to be much contorted. There 

 seems, in fact, to be an intimate connection between 

 excessive disturbance of strata and metamorphism. 

 But by what means were masses of strata many thou- 

 sands of feet thick bent and contorted, and often raised 

 high into the air, so as to produce existing scenic 

 results by affording matter for air and water to work 

 upon ? Not by igneous pressure from below raising the 

 rocks, for that would stretch instead of crumpling 

 strata, in the manner in which we find them in the Alps, 

 Norway and the Highlands, or in less degree in Wales 

 and Cumberland ; but rather because of the radiation 

 from the earth of heat into space, gradually producing a 

 shrinkage of the earth's crust, which, here and there 

 giving way, became crumpled along lines more or less 

 irregular, producing partial upheavals, even though the 

 absolute bulk of the globe was diminishing by cooling 



