T. E. Savage — Relations of the Alexandrian Series. 29 



of the Edgewood is older than any part of the Silurian section 

 of Iowa previously recognized. 



The section given by Keyes* of the Silurian " rocks and 

 their immediate associations as displayed in the deep valley of 

 Noix Creek and elsewhere in the vicinity of Louisiana, in Pike 

 County, Missouri," is misleading in two particulars, (1) because 

 at no place in the valley of Noix Creek or elsewhere within at 

 least eight miles of Louisiana, Missouri, is the member No. 2 of 

 his section a brown limestone ten feet thick, but it is there a light 

 gray oolite, having a maximum thickness of seven or eight 

 feet, the thickness decreasing towards the east and west from 

 Louisiana ; and (2) because an unconformity at the base of the 

 Bowling Green limestone member is apparent only where the 

 oolite phase of the underlying portion of the Edgewood is 

 developed. 



The unconformity below the Bowling Green limestone member. 



The change from the oolite below to the brown magnesian 

 limestone of the Bowling Green member above is abrupt in the 

 vicinity of Louisiana, and farther east across the river in Pike 

 and Calhoun Counties, Illinois ; but about seven miles west of 

 Louisiana, Missouri, near the west border of the oolite along 

 Noix Creek, the oolite passes upward with a gradual transition 

 through two feet of mixed oolite and brown limestone into the 

 brown Bowling Green limestone member without any indica- 

 tion of a sedimentary break. Along the valley of Noix Creek 

 between "Watson Station and Bowling Green, west of the ex- 

 tension of the oolite, the Silurian strata consist entirely of 

 brown limestone, having a thickness of 20 to 25 feet, within 

 which no plane of unconformity can be distinguished. In the 

 vicinity of Edgewood and Cyrene, where the oolite phase is not 

 developed, there is also no apparent unconformity at the base of 

 the Bowling Green limestone member, as shown in the writer's 

 section of the Alexandrian strata near Edgewood. f The 

 unconformity at the base of the Bowling Green limestone 

 member thus appears to be limited to the east side of the area 

 of distribution of the Edgewood formation in this region, where 

 it is underlain by the oolite phase of the Edgewood. 



The oolite is thickest, about seven feet, on the west side of 

 the river in the vicinity of Louisiana and Clarksville, Missouri. 

 It is less than half that thickness farther east, on the Illinois 

 side of the river, where it is succeeded by 9 to 15 feet of the 

 brown Bowling Green limestone. Moreover, in the exposures 

 in Illinois the upper part of the oolite, present in the vicinity of 

 Louisiana and Clarksville, Missouri, is absent. These relations 



*This Journal, vol. xxxvii, p. 254, 1914. 



f Bull. Geol. Soc. America, vol. xxiv, p. 363, 1913. 



