344 The American Geologist. December, 1894 
eal instruments. He also invented a "microscopic compass," 
and an instrument known to geologists as "Locke's Level." 
It was while he was absent in Europe, in 1837. that he was 
appointed one of the assistants on the Ohio survey under W. 
W. Mather, then just established. He took no part in it the 
first year. But his report for 1838 is probably the most val- 
uable contribution to the geology of Ohio which was made 
through that survey, by any single man. It is the most vo- 
luminous and the best illustrated. Prof. Orton, who again 
examined, for the second survey, the region on which Dr. 
Locke reported (S. W. Ohio), had occasion repeatedly to com- 
mend at once the scope and the detail of Locke's first report, 
saying that he had found it correct in observation and in gen- 
eralization. It gives one of the first expositions of the "Blue 
limestone." bringing out clearly the anticlinal form of the 
gentle dips observable along the Ohio river, and showing that 
the coal beds of eastern Ohio, on one side, and of Indiana on 
the other, could not possibly exist in the region of Cincinnati 
except high in the air. at 1,160 feet above Adams county. He 
gives, in connection with a colored map of Adams county, a 
perpendicular colored section of the strata from the coal and 
conglomerate of Scioto county on the east, to the west line of 
Adams county, supposed to pass through West Union. Here 
he represents the Waverly sandstone at the east line of the 
county, 343 feet thick ; followed by a bituminous slate, con- 
taining conspicuous septaria, now known as the Huron shale, 
of Devonian age, 251 feet thick ; Cliff limestone, with basins of 
iron ore, involving in this both the Devonian and Upper Silurian 
limestones, 89 feet thick; marl, 106 feet thick, probably Upper 
Silurian; flinty limestone, 51 feet; clay marl, 25 feet, and 
Blue limestone, 1,000 feet. Although the structure of the re- 
gion is well made out, there is no attempt to assign the strata 
to their respective ages b} T comparisons with other states or 
with Europe. He made an excursion into the coal regions" of 
the southeastern part of the state, and another under the guid- 
ance of Dr. D. D. Owen, to Madison, Ind., for the purpose of 
comparative study of the stratigraphy, particularly to deter- 
mine the manner of junction of the Cliff limestone with the 
Blue. Of the latter excursion he remarks: "For the infor- 
mation of those who may be inclined to make the investiga- 
