222 GEOLOGY OF OHIO. 
follows a tortuous course through sections 35, 36, 37, 25, 20, 21, and 27, 
into sections 28 and 35 of Londonderry. In this latter section the direc- 
tion, previously north-west, is changed to south-east, through 35, 29, and 
22, into 15, 8, and 2 of Oxford, where the course becomes north-east 
through 3 of Oxford into 4 and 5 of Londonderry, from which it crosses 
into 35 of Kirkwood township, Belmont county. Isolated patches are 
found on the western side of the anticlinal in sections 20 and 25 of Lon- 
donderry, 13 and 17 of Madison, and very probably in 10 and 17 of Jeffer- 
son, though in this latter case the coal was not observed. In Guernsey 
county the roof of Coal No. 8 is usually sandstone, sometimes separated 
by a few inches of shale, and the roof-coal is rarely present. Sandstone 
“horsebacks,” of considerable extent, and “clay veins” are of frequent 
occurrence, and have a direction rudely north-east and south-west. The 
thickness of the coal varies little from four feet, and the quality is infe- 
rior to that of coal brought from the river. The strata below this eoal to 
a depth of about one hundred and fifty feet are subject to great and sudden 
variations, sometimes consisting almost entirely of sandstone, while at 
others they are almost wholly shales. 
The Crinoidal limestone, though thin, is an exceedingly important 
stratum. In the Barren Group, where the coals vary abruptly and the 
accompanying strata are for the most part characterless shales and sand- 
stones, the geologist would be frequently at a loss unless some well-char- 
acterized stratum were found marking a definite horizon. Such a guide 
is found in this little limestone, which lies almost midway between Coals 
Nos. 7 and 8, being ordinarily one hundred and fifty feet above the former 
and one hundred and fifty to one hundred and sixty feet below the lat- 
ter. It is usually very hard and impure, weathering into blocks dull 
gray outside, and dingy brown, or light gray, on the freshly fractured sur- 
face. The weathered exterior is covered with plates and spines of cri- 
noids, together with many spines of mollusca. The specimens frequently 
weather entirely free from the rock, and several species common through- 
out the Ohio Coal Measures can be obtained in good condition from this 
stratum alone. Fossils can be collected at Quaker City, at Salesville, at 
several points along the road from Salesville to Washington, as well as 
between Birmingham and Londonderry. The rock is well exposed in 
Millwood, Wills, Center, Knox, Madison, Washington, and Londonderry 
townships. The following is a list of its fossils: 
Crinoidal plates. 
Crinoidal columns. 
ASACTINUSMUCLOSPINUSS see eee eee Reet eee ee eee WC. 
Wophophyllumyproliterumeecree-se eee cece eee eee eee eer bao. M’C., Sp. 
p> So WS 
