SUMMARY 263 



In the western belt the sediments are intensely folded and plicated, 

 and are generally metamorphosed to such an extent that the limestones 

 appear in the form of marble and the argillaceous strata as phyllites. 

 The broad structural lines are in general parallel to the northwest and 

 southeast, but the axes of minor folds are extremely variable in direc- 

 tion. 



The period of mountain-building during which these effects were pro- 

 duced is the earliest of which we have any record in southeastern Alaska, 

 and it was during this epoch that the injection of igneous rocks included 

 under the designation "greenstone 1 ' commenced. Other intrusions of 

 similar basic rocks are known to have occurred also at later dates, as 

 shown by their relatively massive character when compared with certain 

 highty sheared phases of the greenstones. 



In the southern part of the province the Paleozoic sedimentation was 

 interrupted by mountain-building, and also a period of erosion ensued, 

 probably in early Devonian times. The Devonian beds are much less 

 altered than those of the Lower Paleozoic, and the folding which they 

 exhibit is of a broad, open type. Tracing these Devonian beds east- 

 ward, they are found to become metamorphosed as the zone of the Coast 

 Range intrusives is approached. 



The two eastern zones of metamorphic strata which lie adjacent to the 

 intrusive granite belt of the Coast range may be assigned, in part at 

 least, to contact metamorphism. Most of the rocks on the west side of 

 the range are argillites, which are much altered. To the east of the 

 range there is a succession of sediments whose basal members are also 

 considerably altered. This metamorphism is in part plainly clue to 

 igneous contact, but must in part be assigned to the mechanical stress 

 brought about by the intrusion of the granite. The intrusion of the 

 granite has been shown to be Mesozoic and probably post-Triassic. The 

 evidences of contact metamorphism are the minerals, such as garnet and 

 micas, which are developed in a limited contact zone. Mechanical 

 metamorphism evinces itself in the development of shear zones and of 

 foliation as the granite mass is approached. 



During the Mesozoic times and after the injection of the granite large 

 extrusions of volcanic rocks took place. These, as well as the granite, 

 were subsequently somewhat deformed. This deformation was more 

 intense along the axis of the Coast range, where the granites were in part 

 changed to gneisses and mica-schists. Subsequently another intrusion 

 of igneous rocks took place, which, though widely distributed, was not 

 great in bulk. This epoch of injection is represented by the large num- 

 ber of dikes, usually quite massive, which are found in different parts 

 of the region. Deformational movements since Kenai times have been 



