THE LOWER SILURIAN ROCKS. 603 



The quarry on the north side of the marsh, in the X. W. qr. of Sec. 12, Springfield. 

 is on the Madison sandstone, whose upper layers 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 nea-r Madison. Heiny's quarries, on the 

 Lower Magnesian, N. W. qr. Sec. 35, Springfield, are quite extensive. They show the 

 following section: 



Feet. 

 \. Concretionary and brecciated yellow limestone 5 



2. Heavily-bedded white layers with riiuch chert, burnt for lime ... 10 



3. Xo exposure 25 



4. Irregularly thin-bedded, porous, white-and-yellow-mottled limestone (648), with 



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

 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, Midtlleton. The following 

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

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



LOWER MAGNESIAN. 



Ft. In. 



1. Very irregular layers, alternatingly thick and thin, of a brownish-gray, 



close-textured, minutely -crystalline, chcrty limestone (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 limestone, with a thin, sandy layer at top 1 1 



4. Concretionary, cavity- bearing limestone (593), which leaves on solution 



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

 omite crystals 4 4 



5. Yellowish calcareous-sandstone 10 



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



7. Very close-textured, non-crystalline, yellowish 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 (59o, 652), carrying' oolitic 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 limestone 



(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 BEDS. 



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



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

 regular, swelling down and cutting oft' the layers below; in some places 

 cutting oft' also the layers above ; tlu'ckness 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 15 7 



Total 49 6 



