THE ARCHEOZOIC ERA. 141 



it is difficult to distinguish them from pyroclastic rocks and their 

 metamorphic derivatives. 



At a later stage there were great intrusions of molten rock into 

 these surface formations, breaking them up and distorting and meta- 

 morphosing them in greater or less degree. It is not probable that 

 the process of intrusion was distinctly separated from the process of 

 overflow, but the intrusions, as we now find them, must have been 



Fig. 36. — Figure showing the crumpled and contorted structure characteristic 

 of much of the Archean rock. From a Canadian locality. (Ells.) 



preceded by the formation of the rocks into which they were intruded. 

 To a phenomenal extent, the intrusions seem to have taken the form 

 of massive batholiths, so that when the overlying rocks were cut away 

 by erosion, as they have been since, the batholiths came to occupy 

 large areas, and appear, on first study, to constitute a great formation 

 by themselves. They were in fact so interpreted until recently, and 

 seem to make up a large part of what has been called the Laurentian 

 formation. 



