BEDFORD SHALE AT TYPE LOCALITY, TINKERS CREEK, BEDFORD

Bank about 90 feet high, showing 20 feet of the Berea sandstone above and nearly the entire thickness of the Bedford beneath, consisting of blue shale with thin bands of flags or concretions here and there, but with no bluestone and no red shale in the section. On the left is seen the edge of one of the large downfallen blocks of Berea sandstone.

BEDFORD SHALE 2 MILES SOUTH-SOUTHEAST OF BROOKLYN Shows beds of shale with strong dip to the right, overlain by horizontal shales; a thin sandstone layer lies at the summit of the tipped shales.

LEDGES ON TINKERS CREEK JUST WEST OF PENNSYLVANIA RAILROAD BRIDGE Shows the upper 10 feet of the Berea sandstone, overlain by the Orangeville shale, including at base 6 feet of shale representing the Munbury shale velain in t by I font of the Aurorandstone member of the Orangeville shale

View

looking south.

at intervals bands of thin flagstone and of hard, calcareous concretions. Elsewhere it differs materially from this description, and it is the most variable formation in the section.

Distribution and occurrence.-In the Cleveland and Euclid quadrangles excellent exposures of the entire thickness of the formation are found along many streams, notably Euclid, Tinkers, Brandywine, and Skinners Creeks. It is also excellently shown on Big Creek and the two branches of the Rocky River. East of the Cuyahoga a sandstone (the Euclid sandstone lentil) within the Bedford formation caps a terrace averaging half a mile in breadth, the lowest and northernmost one of the three that here constitute the escarpment. This terrace extends up the Cuyahoga Valley as an obscure shoulder on each wall, though narrower and less prominent than at the escarpment front. The sandstone is present as far west as the southwest headwater tributary of Big Creek in the Berea quadrangle, but its terrace has disappeared, and the Bedford forms the foot of the escarpment front and part of the Erie Plain, with a breadth of outcrop of a mile or more. West of the Rocky River the formation lies wholly within the Erie Plain and is so completely covered with drift that little can be told about it.

Character. The Bedford is essentially a soft clay shale, very similar in character to the soft shales of the Chagrin. Much of it is blue, much of it is dull red, and locally some of it is black. West of the Cuyahoga the larger part of the shale is red; east of the river blue prevails. Where both colors occur in the same section the red shale is generally above the blue. The black shale is found only at the base of the formation. Much of the rock is exceedingly dense and firm when freshly exposed and is lacking in fissility, so much so that the excavator usually calls the rock soapstone, as he does also the Chagrin shale. It weathers with extreme rapidity, chiefly by checking into irregular fragments that suggest shrinkage-cracked mud. Fissility develops in some beds but hardly at all in others, and all the material is exceedingly soft and tender when wet, though it becomes fairly firm on thorough drying. The red shale is even weaker than the blue, so that its characteristic occurrence in outcrop is as a red mud, and hand specimens of the firm rock can be collected only when an excavation is being made.

Interbedded with the shales are bands of blue-gray sandstone and of hard dark-gray concretions. (See pl. 3.) The concretionary bands occur at all horizons but are more common near the base. They consist of fine sand and clay, thoroughly cemented by lime and iron carbonates, and there is much variation in the relative amounts of lime and of sand. Mostly they are fine grained and exceedingly hard and flinty. They weather reddish.

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The sandstone bands are usually from 3 to 10 inches thick and occur singly, separated by different thicknesses of shale. Locally they thicken, the interbedded shales becoming very thin, and form a sandstone member from 10 to 25 feet thick in which some very massive beds occur. The stone is light blue-gray, is very fine grained, and contains a considerable quantity of argillaceous matter and a little calcareous matter. The surface of most of the beds is beautifully ripple marked. Such a sandstone (the Euclid sandstone lentil), about 20 feet thick, occurs across the eastern part of the city of Cleveland. It is known commercially as the Euclid bluestone. It extends from Euclid southwestward into and up the Cuyahoga Valley beyond Brecksville but is missing between Newburg and Bedford. It contains massive beds 2 or 3 feet thick, makes an admirable flagstone, and in past years was largely quarried for that purpose, particularly at Euclid. (See pls. 2, B, and 3.) It lies near the base of the formstion, with 2 to 10 feet of blue shale and thin flagstone between it and the Cleveland. Shallow sand channels descend from its base into the shale beneath, and many of them show rounded flow markings very beautifully. The stone contains many concretions, some of marcasite and some of gray lime-iron composition.

In and west of Cleveland many sections show some black shale in the basal part of the Bedford. In the vicinity of Doan Brook a basal bed, about 6 inches thick, of dense gray-black nonfissile shale, which is coarser grained than the ordinary Cleveland shale, seems to grade upward into the overlying blue shale, has a sharp contact with the ordinary Cleveland beneath, and carries invertebrate fossils that are also found in the next succeeding shales with the typical Bedford fauna. It has every appearance of being reworked black mud, and on this account it is included in the Bedford shale instead of in the Cleveland. On Mill Creek is a similar zone only 2 or 3 inches thick, which has already been described. The greatest known thickness of these black beds in the Bedford is found in the Skinners Run section, where they contain sandstone bands and lenses identical in character with the usual Bedford sandstones and have a thickness of more than 25 feet.

Variation. The Bedford shale shows great variation in character and in thickness from place to place within the district. The Euclid Creek sections show about 15 feet of basal blue shale with thin flags, on which lies about 25 feet of Euclid sandstone, capped by 30 to 50 feet of shale, the upper 10 to 15 feet of which is usually red and the remainder blue. (See pl. 4.) The Doan Brook and Mill Creek sections are very similar. The Tinkers Creek section differs materially. No red shale is present, and the whole 85 feet consists of blue shale with thin courses of flagstone and here and there a concretionary band. The zone from 40 to 65 feet above the base contains much more