THE PROTEROZOIC ERA. 



183 



The Animikean system. 



(The Upper Huronian of some authors.) 



General relations. — After erosion had long operated on the de- 

 formed Huronian rocks, much of the area about Lake Superior again 

 became the site of deposition. The change was probably brought 

 about by slow subsidence, and as it progressed, the sea appears to 

 have encroached upon the areas which, while land, had suffered ex- 

 tensive erosion. Meanwhile great areas of the earth's surface" prob- 

 ably remained continuously under water, and were the sites of deposi- 

 tion. Sedimentation was renewed in the Lake Superior region, prob- 

 ably under conditions similar to those which existed at the beginning 

 of the Huronian period. With the renewal of sedimentation, there was 

 begun a second series of sedimentary beds lying on the eroded sur- 

 face of the first. 



While the Animikean series is, as a rule, unconformable on the 

 Huronian where their contact is seen, it does not follow that this is 



Fig. 66. — Diagram showing same area as Fig. 62, after subsidence, which allows of 

 sedimentation over a part of the eroded surface of H. At the right the sediments 

 b are conformable on H; at the left, sediments A are unconformable on H. 



their universal relationship. Wherever the Huronian formations were 

 not exposed to erosion before the deposition of the next succeeding 

 series, their relation to the Animikean must be one of conformity. 

 The area of conformity, the whole earth considered, must be far greater 

 than the area of unconformity, though the latter is the rule where 

 the contact of the two systems is known. In some parts of the Lake 

 Superior region the subsidence of the Animikean period appears to have 

 been so great that the sea covered the whole of the Huronian series, 

 and reached the Archean beyond. In such places Animikean sedi- 

 ments were deposited on the Archean. 



Composition. — The source of material of the Animikean system is 

 readily understood. All the exposed Archean and all the exposed 

 Huronian formations probably made their contributions. Sediments 



