SUPPLEMENTAL REPORT — HANGING ROCK DISTRICT. 8S5 



Coal Measures. It can be followed without the slightest uncertainty 

 from the Ohio Valley as far at least as Bristol, Perry county. 



4. Shawnee Limestone.— The Shawnee, or Bufi' Limestone, is the next 

 of the main series to be reached in ascending the scale. Its average 

 elevation above the Gray Limestone in the Hocking Valley is one hun- 

 dred and ten feet, but the distance increases somewhat to the Eoufrhward, 

 becoming one hundred and thirty or one hundred and forty feet in Law- 

 rence county. This limestone is a persistent, though not very conspicu- 

 ous member of the geological scale of the Hanging Rock District. It 

 takes its name from Shawnee, Perry county, where it is exteasiyely 

 worked for furnace flux. It is also largely worked for the same pur^ 

 pose in the Monday Creek and Snow Fork valleys. Its thickness 

 varies between one and three feet, but it falls below two feet much 

 oftener than it rises above this measure. 



Its color is described by the name by which it is generally known, 

 viz., the Buff Limestone. The best varieties of it carry ninety-three per 

 cent, of carbonate of lime and only four or five per cent, of silica, bu !; it gen- 

 ally contains ten or fifteen per cent, of silicious matter and not more than 

 eighty to eighty-five per cent, of carbonate of lime. The amount of iron 

 and alumina often rises to ten or fifteen per cent, and a small percentage 

 of manganese is a constant element. The best varieties of it are not 

 surpassed in purity by any limestone in the district, but it is unsteady 

 in copaposition. It is commonly called non-fossiliferous, as it lacks the 

 usual coal measure forms, but fragments of crustaceans are not of rare 

 occurrence in it. It never passes into flint, as the limestones previously 

 described so often do. On the whole, it is an excellent and reliable guide 

 to the geology of the district to which it belongs. The only uncertainty 

 in regard to it that is likely to occur, results from a duplication of 

 this portion of the series in some parts of the district. From twelve to 

 twenty feet above the Shawnee Limestone, and about the same distance 

 below, two other Bufi" Limestones are sometimes found, but they are of 

 more interest as ore beds than as limestones, and will be treated on a 

 subsequent page under that head. 



5. The Cambridge Limestone.' — The fifth member of this orderly series 

 of limestones is the strptum called the Cambridge Limestone by 

 Prof. Andrews. The aame is derived from the village of Cambridge, 

 Guernsey county, where this limestone is said to be well developed. 



The Cambridge Limestone has long been recognized as one of the most 

 persistent of our Coal Measure limestones. It stretches through every 

 county of Ohio in which its proper horizon is reached, and furnishes an 

 invaluable guide in the determination of the order of the Lower and the 

 Barren Coal Measures. . The geologists of the first' survey eaw its avail- 



