F. H. Lahee — Metamorphism and Geological Structure. 367 



SE. 



Rectangle : 

 Stage A : 

 Stage B : 

 Stage C : 

 Stage D : 



Conglomerate Sandstone Shale Coal Totals 





 2 



10 

 o 



5 



6 

 10 



1 



7 

 18 

 26 



3 



Totals : 



14 



16 



22 



2 



54 



SW. Rectangle : 

 Stage A : 

 Stage B : 



1 







1 

 



1 



2 





 



3 



2 



Stage C : 

 Stage D : 



5 

 3 



7 

 14 



14 

 13 



1 







27 

 30 



Totals : 



22 



30 



62 



The relative number of examples of each stage for each 

 rectangle may be calculated on a percentage basis : 



Eectangle 



Stage A 



Stage B 



Stage C 



Stage J) 



Total 



NE. 



14-286^ 



66-667$ 



19-047$ 



Ofc 



100-00$ 



NW. 



32-143 



14-286 



46-428 



7-143$ 



100-00 



SE. 



12-963 



33-333 



48-148 



5-555 



100-00 



SW. 



4-918 



3279 



42-623 



49-180 



100-00 



Grouping Stages A 

 together, and Stages C 

 together : 



and B (rather low metamorphism) 

 and D (rather high metamorphism) 



Eectangle 



NE. 

 NW. 

 SE, 

 SW. 



Stages A and B 

 80-953$ 

 46-429 

 46*296 



8-197 



Stages C and D 

 19-047$ 

 53-571 

 53-704 

 91*803 



These figures demonstrate plainly that the degree of meta- 

 morphism in the southern half of the Basin increases west- 

 ward and southward.* 



Relations between the Degree of Metamorphism and 

 Stratigraphic Depth. 



This subject may be approached in two ways : we may study 

 specimens brought up from known depths in borings or in 

 mines, or we may examine surface outcrops of which the strati- 

 graphic position is at least fairly certain. 



(1) In regard to the first suggestion, Professor Wood worth-f- 

 elted the statement of Professor Collier Cobb, that " the 



* We have already suggested that the western coals are most highly meta- 

 morphosed. See p. 356. 



t Shaler, N. S., Woodworth, J. B.,and Foerste, A. F. : op. cit., p. 191. 



