CHAPTER yi. 



ElilSUMEl OF JHE GEOLOGICAL FOEMATIONS OF THE DIS- 



TEIOT. 



Arch^an Eocks — Paleozoic Eocks— Mesozoic Eocks— Post-Cretaceous— Ceno- 

 zoic Eocks — Volcanic Eocks. 



In tlie present chapter I propose to review briefly the geological 

 formations, and to state a few conclusions that appear obvious from a 

 consideration of the facts presented in the preceding portions of the 

 report. These facts are as yet too isolated, and the district too cursor- 

 ily examined to afford relial3le data for extended generalizations. 



As is evident from the preceding chapters, the district is almost entirely 

 a sedimentary area. In the northeastern corner we have Archaean rocks 

 in the foothills of the Wind Eiver Mountains, but the area is very lim- 

 ited. In the northwest the basaltic flows are somewhat prominent, ^o 

 other volcanic rock was noted within the limits of our district. The sedi- 

 mentary rocks are much folded in tlie eastern portion of the district, 

 and accompanying this folding there was much vertical displacement. 

 Toward the west the folds have been very much eroded, and the spaces 

 between the portions left have been filled with lake deposits. The fol- 

 lowing table of the formations of our district j)resents the general section 

 as derived from the detailed sections already given: 



611 



