CHARACTER OF SILURIAN FORMATIONS 405 



Variations in Osgood bed. — The Osgood bed, at its most northeastern 

 exposures, is a clay shale. It here also presents its greatest thickness : 

 22 feet at the S. R. Wood locality (locality 2) and 20 feet at Bledsoe 

 (locality 3). 



South westward it changes its lithological character rapidly. At South 

 Tunnel (locality 4) the clay is more indurated and calcareous, espe- 

 cially near the top of the bed. The more shaly and the more indurated 

 layers are interbedded, producing a banded appearance. The total 

 thickness of the Osgood bed at this point is 14 feet. 



At Baker (localit}^ 6) the upper part of the Osgood bed is sufficiently 

 indurated to be quarried, although the rock disintegrates so readily that 

 its use is to be discouraged. The upper half of the indurated beds be- 

 comes a crinoidal limestone at the south end of the quarry. The indu- 

 rated rock is 7j feet thick. It is underlaid by 6k feet of soft clay shale, 

 best exposed above the Clinton ledge at the southern end of the quarry. 

 The total thickness of the Osgood bed at this locality is therefore 14 feet. 

 The presence of the crinoidal material in the upper part of the section 

 makes it difficult to distinguish the top of the Osgood bed from the base 

 of the Laurel limestone. 



This difficulty increases on going southwestward. At Whites Bend 

 (locality 8) the larger part of the Osgood bed is soft and weathers read- 

 ily, but near the top the clay becomes more indurated and calcareous, 

 and gradually merges into the overlying Laurel limestone. It is impos- 

 sible to determine the precise line of separation between the two for- 

 mations. 



The best exposure of the Osgood bed near Newsom (locality 12) is 

 along the road following the north side of the Harpeth river westward 

 toward Foster and Creighton switch. The clay section is here 11 feet 

 thick. The lower 2 feet are purplish colored, and the immediately over- 

 lying beds are more or less tinged with the same color. The shaly char- 

 acter of the Osgood formation has largely disappeared. It has more the 

 appearance of a soft clay rock, the layers of which are not sufficiently 

 thin to give it a distinctly shaly character. At the top the bed is more 

 indurated, and is not readily distinguished from the Laurel limestone. 

 This is true also at the quarry along the railroad, an eighth of a mile 

 west of Newsom. Here the quarry rock (Laurel) is underlaid by 1 foot 

 of soft limestone, readily weathering; then 1 foot of limestone, and 6i 

 feet of indurated clay, harder near the top, undoubtedly belonging to 

 the Osgood bed. These exposures form a transition to those south of the 

 Harpeth River valley, where the Osgood bed is represented by soft lime- 

 stones, readil}^ disintegrating. 



South of the home of Johnson V. Linton (locality 15) 21 feet of Laurel 



