,7.10 J. S. DILLER — GEOLOGY OF THE TAYLORVILLE REGION. 



Grizzly Anticlinal. — The existence of the Grizzly anticlinal is not so 

 clearly defined as that of the Genesee, for its determination depends 

 upon the presence of one fossiliferous stratum, viz, the Montgomery lime- 

 stone (Silurian). The strata immediately adjoining this limestone on 

 both sides are in general much more ancient looking than those coming 

 next in order, and if we proceed far enough across the strike in either 

 direction from the Silurian the first fossiliferous strata met with on hoth 

 sides are much younger. Toward the northeast we need to proceed 

 only a short distance, for the Jura, as shown in figures 1 and '.), appears 

 at the very foot of mount Grizzly; hut in the opposite direction the dis- 

 tance is much greater. Although the limestone of the Shoo Fly beds 

 contains a few crinoids, no determinable fossiliferous strata are met with 

 in that direction before reaching the Hosselkus limestone (Triassic) near 

 the mouth of Rush creek. 



Fnii'RE 9. — Northeastern Slope of Grizzly Mountain. 

 8 = Hardgrave sandstone; 14 = Shoo Fly beds ('.'): 17 = Montgomery limestone; 18 = Grizzly 

 quartzite ; E= Eruptive rocks. 



The distance from the Silurian to the Hosselkus limestone on the 

 eastern side of the arch is about two miles, for. as we have shown, it lies 

 unconformably beneath the middle portion of mount Jura, hut in the 

 opposite direction the distance is at least eight times as great. 



While in the Genesee anticlinal the middle of the arch is clearly de- 

 fined by the Carboniferous, which is flanked on hoth sides by the 

 Triassic, in the Grizzly arch the noddle formation is less evident. The 

 oldest stratum known positively by its fossils is the Montgomery lime- 

 stone, which appears in the very crest of Grizzly mountain (figure 9). 

 It dips southwestward , overlying the drizzly quartzite, and is itself 

 overlain by the Taylorville slates. As the Grizzly quartzite is not the 

 equivalent of the Taylorville slates, it is evident that the Montgomery 

 limestone is not the middle formation of the anticlinal. A careful 

 scrutiny of the folded strata on the measured section does not disclose 

 any repetition which would locate the middle of the arch. 



The crest of a mountain developed by erosion of an overturned anti- 

 clinal is generally formed of hard strata within the upper or long limb 



