340 THE CAMBRIAN. [bull. 81. 



In Madison, St. Francois, and Iron Counties, Prof. G. C. Broadhead 

 found beneath the third magnesian limestone the following downward 

 succession : 



(3) Siliceous or grit-stone bed, with intercalated magnesian lime- 

 stone. 

 (2) Marble beds. 



(1) Sandstones, conglomerates, and shales. 

 In No. 3 Lingalella lambomi Meek has been found. The marble 

 beds or No. 2 appear to be confined to the southwest quarter of Madison 

 and the central and northern parts of Iron and extend into Reynolds 

 County. The greatest thickness is not over 30 feet, and they are not 

 always present. 



No. 1 is confined chiefly to the northern part^of Iron and Madison, extending to St. 

 Francois. The entire thickness of this as well as the regular order of its various 

 beds is rather difficult to arrive at. But we find both in Iron and Madison Counties 

 coarse conglomerates resting on granite and porphyry. We also find sandstones, 

 which are sometimes very coarse, and at other times fine grained, resting on con- 

 glomerates. We also find shale or slate beds reposing on granite and underlying sand- 

 stone. Similar shale beds are also intercalated with the sandstone. In the neigh- 

 borhood of Mine La Motte this sandstone reaches to over 100 feet in thickness, and 

 is also found to be the Jowest rock directly resting on the granite. Borings with 

 diamond -drill on the Mine La Motte property indicate magnesian limestone, with some 

 siliceous beds, 80 feet; sandstone, 63 feet; granite. 



On St. Francois River, in Madison County, these lower sandstones rest directly on 

 the granite and are unaltered; on Twelve-Mile Creek, Madison County, the marble 

 beds and sandstones rest unaltered on the porphyry, and on Big Creek, Iron County, 

 heavy beds of unaltered magnesian limestone rest directly on the porphyry. 1 



At the deep well of the St. Louis County insane asylum, beneath the 

 third magnesian limestone, the drill passed through, going down — 

 98 feet of third sandstone. 



384 feet of fourth magnesian limestone. 

 54 feet of Potsdam sandstone. 



At the base of the sandstone it entered what was supposed to be 

 granite, although the line of demarkation between the sandstone and 

 the granite was not well defined. 2 



In the descriptive geology of Madison County Prof. Broadhead states 

 that the sedimentary rocks were deposited across the valleys between 

 the mountains and the hills (that is, of the old pre-Cambrian land sur- 

 face). The order of deposition, commencing at the oldest, is — 



(1) Sandstones, conglomerates, and shales. 



(2) Marble beds. 



(3) Grit-stone beds and rough beds of magnesian limestone. 

 Above this comes the magnesian limestone referred to the Calciferous. 

 In the vicinity of Fredericktown there is a series of grits between the 



grit-stone beds and the superjacent magnesian limestone in which Lin- 

 gtilella lambomi has been found. It is stated that in the lower portion 



1 Geological Survey Missouri, including field work of 1873-1874, vol. 1, 187*, pp. 31, 32. 

 ! Op.cit, p. 32. 



