THE PROTEROZOIC ERA. 



185 



show that they were deformed and metamorphosed when they lay 

 far (probably many thousand feet) below the surface. It is impos- 

 sible to estimate in years, even approximately, the duration of the 

 period, but it may well have been as great as that of the Huronian. 

 Deformation and erosion. — After the Animikean formations had 

 attained great thicknesses, the bed on which they rested suffered wide- 

 spread, but not universal, deformation, and as the- sea receded from its 

 former shores it exposed a surface covered by the new formations. So 

 soon as they emerged from the sea, they were subject to erosion (Fig. 67). 



Fig. 67. — Diagram showing same area as Fig. 66 after the Animikean beds, A, have 



been deformed and eroded. 



The sediments worn from them were carried down to lower levels and 

 deposited; but the sites of deposition during the early part of this erosion 

 interval have not been seen, or, if seen, have not been recognized. 

 The deformation winch inaugurated the period of erosion was probab.y 

 slow, and the area converted into land seems to have remained above 

 the water for a period of time long enough to allow of extensive erosion. 

 Its amount cannot now be accurately measured, but it is certain that 

 thousands of feet of rock were removed from the surface of the Ani- 

 mikean system in many places. 



Alteration of the rocks. — -In general the rocks of this system have 

 been less metamorphosed than those of the preceding. This fact, as 

 well as the attitude of the strata, indicates that they have been subject 

 to less dynamic action. In some regions, as on the north shore of 

 Lake Superior, the strata are still approximately horizontal; in others, 

 as on the south shore of Lake Superior, they are notably deformed 

 (Figs. 68 and 69). The forces involved in the transformation of the 

 Animikean beds affected the Huronian systems at the same time, and 

 the metamorphism of the latter may be in part the result of changes 

 effected during the deformation of the former. But while the Amini- 



