WcatJieriiig of Diabase in Virginia. — Watson. 85 
by the rivers in their present arrangement and past behavior; 
the disposition of the formations in encirchng belts skirted 
by detached outliers; the positive evidence of fault scarp re- 
movals; — we may conclude that denudation and not lack of 
deposition of the later formations is the true explanation of 
surface Ordovician in the Ohio valley; and that the "Cincin- 
nati Silurian island" must hencforth take rank as a geologic 
mvth. 
WEATHERING OF DIABASE NEAR CHATHAIVI. 
VIRGINIA.* 
By Thomas L. Watson, State Geol. Survey, Atlanta. Ga. 
Introduction. \ 
While visiting Virginia during the late summer and early 
fall of 1897, the writer had occasion to study and collect 
specimens of the so-called Mesozoic "trap rocks," which have 
been noted in the form of sheets and dikes throughout the 
most of the Atlantic border region. 
Notwithstanding the rather complete knowledge of the 
geological features and chemical composition of these rocks, 
but few writers have touched on their disintegration and de- 
composition. Wherever studied along the Atlantic border 
region, their remarkable uniformity has been noted, varying 
but little in mineral and chemical composition. Futhermore, 
the specific gravity determinations collected from various 
sources and quoted by professor James D. Dana J further 
illustrate the striking uniformity in these rocks, the limits of 
which are given as 2.94 and 3.16. 
*The writer wishes to acknowledge his indebtedness to the authorities 
of the United States National Museum for kindly allowing him the op- 
portunity to work up the material. He is especially indebted to pro- 
fessor Geo. P. Merrill, Head Curator, Dept. of Geology, in the Museum, 
for so generously placing at his disposal facilities and equipment for the 
prosecution of the work, as well as for the constant suggestions given 
throughout. To Dr. E. C. E. Lord, I am indebted for many sugges- 
tions and aid. 
fThe results of this investigation are based upon the methods and 
principles so clearly set forth by Dr. George P. Merrill in his numerous 
valuable publications on rock weathering. See Bull. G. S. A.. Journal 
of Geology, Treatise on "Rocks, Rock-Weathering and Soils." 
$Am. Journ. Science, 1873, (3. S.) 6, 105. 
