THE LOWER SILURIAN ROCKS. 603 



The quany on the north side of the marsh, in the N. W. qr. of Sec. 12, Springfield, 

 is on the Madison sandstone, whose upper ki,yers here are heavy, regular, buff-colored, 

 contain over 40 per cent, of soluble ingredients, and make a good building stone, re- 

 sembling that quarried at the same horizon near Madison. Heiny's quarries, on the 

 l/ower Magnesian, N. W. qr. Sec. 35, Spring-field, are quite extensive. They sliow the 

 following section: 



Feet. 



1. Concretionary and brecciated yeUow limestone .- 5 



2. Heavily-bedded white layers with litask «hert, burnt for Hme 10 



3. Nb exposure..,,^ 25 



4, Inegnlarly thin-bedded, porous, white-and-yellow-mottled limestone (648), vrith 



geodic cavities, many black dendritic markings, and 6.11 per cent, of msoluble 

 ingredients 15 



The lowest exposure is near the base of the formation. 



The Madison sandstone and overlying Lower Magnesian are finely exposed in a large 

 quarry on the edge of the high land, S. E. qr. Sec. 11, Middleton. The following 

 section, taken here, is interesting as shovring how the great Lower sandstone series 

 graduates upward into the Lower Magnesian; the order is as usual a descending one: 



LOWER MAGNESIAK. 



.Ft. In. 



1. Very irregular layers, altematingly thick and thin, of a brovniish-gray, 



dose-textured, miautoly-crystalluie, chcrty hmestone (591), which leaves 

 on solution 4.39 per cent, of a very fine, clayey residue; 7 feet below the 

 top is a marked concretionary layer, one foot thick 18 4 



2. Brecciated lay-er of sandy, grayish limestone (592), containing 63.89 per 



cent, of fine gray quartz sand 1 . • 



3. Thick layer of gray, flinty-textured hmestone, with a thin, sandy layer at top 1 1 



4. Concretionary, cavity- beariag Hmestone (593), which leaves on solution 



11.03 per cent, of fine, grayish, aluminous residue; the cavities cany dol- 

 omite crystals • 4 4 



5. Yellowish calcareous-sandstone 10 



6. Yellowish limestone, in places quite sandy 2 . . 



7. Very close-textured, non-crystalline, yellovfish limestone (594), containing 



9.19 per cent, of fine, aluminous, insoluble matter, and much marked by 

 dendritic oxide of manganese 2 2 



8. Brownish, sandy, porous limestone (595, 652), carrying oohtic chert, numer- 



ous crystal-lined cavities, and containing 28.04 per cent, of sand 2 2 



9. Yellow-and-gray-mottled, rough-textured, conchoidal- fracturing hmestone 



(596), containing 3.89 per cent, of aluminous impurities 1 . . 



10. Oolitic chert layer (597; nearly pure quartz, only .01 per cent, being solu- 



ble 6 



MADISON BBHS. 



11. Pure white, exceedingly fine sandstone (598, 651), composed of angular to 



rolled grains of translucent quartz; often loose sand; the layer very ir- 

 regular, swelhng down and cutting offtlie layers below; in some places 

 cutting off also the layers above; thickness varies from 7 inches to 1 5 



12. Light yellow, friable, fine-grained, dolomitic sandstone (599, 650), composed 



of rolled quartz grains embedded in a crystalline dolomitic matrix; the 

 sand being 63.4 per cent, of the rock; the exact equivalents of the Mad- 

 ison building-stone; thickness ^ "^ 



Total 49 6 



