POTSDAM SANDSTONE. 



265 



Fig. 24. 



servations elsewhere, that the whole slope is underlaid by the Madison sandstone. Thick- 

 ness 30 feet. 



3 Rotten calcareous chipstone, occupying the surface of the lower terrace, derived by 



disintegration from a rock similar in char- 

 acter to the stratum below. Thickness 3 

 feet. 



4. Light butt', thin bedded, impure, gran- 

 ular, porous, soft, easily fractured magne- 

 sian limestone, marked with fucoidal impres- 

 sions and interlaid with thin seams of green 

 sand. Examined under the microscope, the 

 component grains appear very angular and 

 in the dry state mostly opaque. On the addi- 

 tion of acid, part are dissolved with efferves- 

 cence, leaving many transparent angular 

 particles insoluble in warm acid. Used for 

 building purposes. Thickness 8 feet. 



5. Unexposed, 4 feet. 



6. Greenish and grayish, scarcely cohe- 

 rent sandstone, composed of white or light 

 colored grains of quartzose sand and green 

 grains of glauconite. Thickness 6 feet. 



7. Calcareous, banded and mottled white 

 and orange, coarse granular, sandrock, part- 

 ly formed of quartz grains and partly of 

 small crystals of dolomite. Thickness, 5% 

 inches. 



8. Soft, white, very friable, quartzose sandstone. Thickness, 2 feet and 5 inches. 



9. Calcareous layer of mottled, greenish and orange color, coarse granular, uneven 

 texture and medium hardness, graduating into the green sand below. Thickness, 9 

 inches. 



10. Green sand of deep color, speckled" with reddish iron stains, very friable, gradu- 

 ating into the layer above. Thickness, 21 inches. 



11. Porous, granular, crystalline dolomitic layers, marked by nodules of hematite. 

 One layer is 7% inches thick, and firm and excellent for building purposes. The layers 

 are separated by thin seams of green sand. Thickness, 3 feet and 6 inches. 



12. Greenish white sandstone containing spherical concretions and Scolithus tubes. 

 The walls of the tubes are usually cemented with iron oxide and the fossil stands out 

 beautifully on the weathered surfaces. Thickness, 6 feet. 



13. Orange yellow, calcareous sand rock, containing crystals of calcite. Thickness, 

 13 inches. 



14. Sandstone, containing spherical concretions. Thickness, 4 feet. 



15. Orange yellow, calcareous rock, as above. Thickness, 1 foot. 



16. Dirty greenish white sandstone, full of the spherical concretions and blotched 

 with iron stains. Thickness, 3 feet. 



17. Orange yellow, calcareous rock, with calcite crystals imbedded. Thickness 15 

 inches. 



18. White friable sandstone, the upper foot filled with concretions, the lower three 

 and one-half with Scolithus. Thickness, 4 feet and 6 inches. 



19. A layer consisting of quartzose sand cemented by calcareous material, containing 

 calcite crystals, and marked with linionite. Thickness, 8 inches. 



20. Sandstone filled with concretions. Thickness, 8 inches. 



PBOFILE SECTION OP BABTHOLOMBW'S 

 BLUFF. 



