GEOLOGICAL SCALE AND STRUCTURE. 15 



Though the last to be recognized of our several limestone forma- 

 tions, the Waterlime occupies a larger area in Ohio than any other, its 

 principal developments being found in the drift covered portions of the 

 northwestern quarter of the state. It has also a much greater thickness 

 than any other limestone of the state, its full measure being at least six 

 hundred feet, or twice the greatest thickness of the Niagara limestone 



It can be described as, in the main, a sti ong, compact, magnesian 

 limestone, poor, as a rule, in fossils, and often altogether destitute of 

 them for considerable areas, microscopic forms being excepted. It is, 

 for the most part, drab or brown in color ; but occasionally it becomes 

 very light-colored, and again it is found dark blue in color. Throughout 

 much of its extent it is brecciated, the bed seeming to have been broken 

 into sometimes small and sometimes large angular fragments after their 

 hardening, and then to have been recemented without further disturbance. 

 In addition to this, it contains an immense amount of true conglomerate, 

 the pebbles, many of which are bowlders rather than pebbles, being all 

 derived from the rocks of the same general age, but frequently differing in 

 color from the matrix. A bowlder weighing a ton or more has recently 

 been found in central Ohio, which was broken irom the conglomerate 

 phase of this formation. The most striking exhibitions of this phase are 

 found in Lucas county. The surface of many successive layers at numer- 

 ous points are covered with suncracks, thus furnishing additional proof of 

 having been formed in shallow water near the edge of the sea. In such 

 localities the beds are usually quite thin and are also impure in composi- 

 tion. In these respects, this phase suggests the conditions of the Onon- 

 daga vSalt Group of New York. These features are very characteristic 

 ones. A rude concretionary structure is also quite distinctive of the beds 

 of this age. The Waterlime in Ohio everywhere contains petroleum in 

 small quantity, which is shown by the odor of freshly broken surfaces. 

 No noteworthy accumulations of oil or gas have thus far been found 

 within it. At some points it carries considerable asphalt, distributed 

 through the rocks in shot-like grains, or else in sheets and films. Thin 

 streaks of carbonaceous matter traversing the rock parallel to its bed 

 planes are one of the constant marks of the stratum in Ohio It is 

 generally thin and even in its bedding, but in some localities it contains 

 massive beds. At some points, as at Greenfield, Highland county, it is 

 remarkable for its evenness, and great value is given to the formation on 

 this account, when combined with other qualities already named. It is 

 frequentl} T a pure dolomite in composition and accordingly it yields mag- 

 nesian lime of high quality and is extensively burned in the state, rival- 

 ing in this respect the Guelph beds of the Niagara. In southern Ohio it 

 has a maxim am thickness of one hundred feet, and here it reaches its 

 highest quality in all respects; but in central and northern Ohio it attains 

 the great thickness previously reported. There also, it contains several 



