WALCOTT.] 



SUMMARY MONTANA. 



Silurian section. 



323 



a 



a 







Blue and gray limestones, with characteristic 

 Quebec fossils. 



+ 

 o 



© 

 ©^ 



■is 



© 

 © 



1 



oo 



MS? 



6H 



C3 



a 



O 



d o 

 O 





Blue limestones, generally laminated, with al- 

 ternations of greenish sandstones and shales 

 and siliceous slates. 



4 



© 

 © 



a. 2 



.2 '*"' 



QQ 





s 



ao 



O 

 Pi 



d S 



31 



Pink and white quartzites, conglomeritic at 

 top, with thin layer of limestone at the base. 



+ 



© 



© 

 © 



+ 



© 

 © 

 ©^ 







a 

 .2 



o 



ao 

 0) 



ea 



1—1 



00 



.2 

 "C 



a 

 o 



Olive green and gray chloritic slates and in- 

 durated clay slates. 



© 



CO 

 r-T 



.2 



IS 

 of 



H 



O 



a 



Silvery and steel-gray micaceous slates. 



43 



© 

 © 



a 

 .2 



o 

 a 



S3 



Dark quartzites with interlaminated slates. 



© 

 © 



OQ 





a 



c3 



"a 

 o 







w 



5 

 O 



Red quartzites and qunrtzitic sandstones, with con- 

 gloineritic and shaly layers. 



© 

 o 

 w 



3 



© 



5* 



t-T 



0* 



CO 

 1— I 



CI 



.2 





Limestones. 



C3 



93 



of 



CO 





Very dark green chloriiic schists, containing quartz 

 and serpentine seams and interlaminated bands of 

 metamorphosed argillaceous slates, and a band of 

 pink quartzite '200 feet thick. 



© 

 © 



© 



ft 



a 

 

 •r-i 



© 



In copying the table it has been reversed, so as to follow the nat- 

 .ural order. As interpreted in the light of our present knowledge of 

 the Cambrian rocks in the Rocky Mountains, the Quebec and Calcifer- 

 ous of this section are referred to the Upper Cambrian. Whether the 

 rocks referred to the Potsdam and Acadian are of Cambrian age or not 

 will remain undetermined until some paleontologic proof is obtained. 



MONTANA, 



As far as known, the Cambrian rocks of Montana are restricted to the 

 southern portion of the State. Two areas are well defined, one about 

 the northern end of the Big Horn range and the other within the area 

 drained by the Gallatin and the Yellowstone Eivers. 



