Pittsburgh Coal Strata. 69 



2. Sandstone ; fine grained ; ash colored ; the upper portion of 

 the deposit very argillaceous, like marl or ochre ; becoming more 

 arenaceous and solid as it descends ; structure, slaty. — 30 feet. 



3. Dark brown, carbonaceous shale ; slaty structure, with im- 

 pressions of leaves of Arundinaceous, Neuropterous, and various 

 other species of plants, detached and scattered through and between 

 the layers. It decomposes into a brown clayey earth, when expo- 

 sed to the influence of the atmosphere. — 4 feet. 



4. Dark colored, carbonaceous clay ; plastic and not stratified in 

 laminae; very heavy and compact; reposing on the coal, and com- 

 mon to this deposit through all this region, being No. 3. of the " Il- 

 lustration." — 6 feet. 



5. Bituminous coal ; of a fine quality ; burning with great free- 

 dom. This bed has been worked through the hill at this spot, the 

 distance of half a mile, and has a moderate dip to the S. E. suffi- 

 cient to drain the mine. It is found in all the adjacent hills at near- 

 ly the same elevation, and is the main deposit for supplying the city 

 of Pittsburgh with all its numerous manufactures. Its specific grav- 

 ity is 1.28. In deflagration with nitre, twenty four grains will de- 

 compose one hundred of nitrate of potash, which will give it about 

 50 per cent of charcoal ; there being some variation in different parts 

 of the bed. — 6 feet. 



6. Dark, slaty clay ; splitting into thin laminae near the top of 

 the deposit and becoming thicker and more compact below. This 

 bed contains fewer fossil plants than the one above the coal. — 5 feet. 



7. Sandstone ; ash colored ; in thin beds of from four to twelve 

 inches in thickness. — 10 feet. 



8. Dark colored limestone, in beds of three or four feet in thick- 

 ness ; no fossil shells observed. — 10 feet. 



9. Sandstone ; light colored and argillaceous, deposited in beds 

 of from three to five feet in thickness. These sandstone deposits, all 

 contain in greater or smaller numbers, casts and impressions of plants. 

 A drawing of one, " calaraites cannoeformis," is given on figure No. 

 35 page 23 of the wood cuts, and on No. 65 p. 29, probably an 

 Equisetum, furnished by R. Peter, M. D. to whom I am indebted 

 for many valuable facts. In other places, broad flat leaves, in great 

 profusion, are replaced by or changed into carbon. A fossil, fluvia- 

 tile unio, w-as taken from the. sandstone rock, about twenty miles up 

 the Monongahela, where many impressions of coal plants are found 

 in the slaty shale. In excavating the canal tunnel through " Grant's 



