Baltimore and the Ohio River. pisly| 
dip and direction of the rocks on both sides of the stream, are suffi- 
ciently evident to convince me that the limestone does in reality pass 
under the slate. Perhaps, if this had been the only case of the kind, 
I might have hesitated still longer before drawing the above conclu- 
sion; at least I might have been tempted to distrust my eyes or close 
them, but farther examination saved me from the dilemma; the case 
proved afterwards of comparatively frequent occurrence, and 1 am 
now fully persuaded, that all the limerock between the Monocacy 
and Cumberland, exists in strata alternating with those of the gray- 
wacke formation, and that it is interstratified with the slates and sand- 
stones of that formation. ‘To one who has examined only the limestone 
vallies, this view may appear to underrate their importance and ex- 
tent. But in reality they are by no means as important as might be 
supposed, as will be evident by inspecting the section. I have there 
endeavored to give, as accurately as I could, the relative extent, lon- 
gitudinally, of each formation, and we can there see how the limerock, 
extensive as it may be, dwindles in importance, when compared 
with the still more extensive graywacke. ‘This view also renders 
more intelligible the dip of the limerock in Frederick and Ha- 
gerstown vallies, which otherwise would be rather inexplicable. In 
both it is towards the S. EK. while the strata of the mountain ridges, 
separating the two vallies, is also towards the S. E. and the nearest 
slate east of Frederick city and west of Hagerstown also inclines in 
the same direction. Similar alternations also occur at other points 
along the section, and will be noticed in their place. It has happen- 
ed that the actual contact of the limerock and overlying slate, has not 
been as plainly seen along the line of the section as at points a little 
on either side. A few rods east of Martinsburg, Va., the limerock 
on which that town is built, (and which is undoubtedly a continuous 
formation with that crossed by the section at Hagerstown,) may be 
seen, distinctly passing under the slate bordering the Opequon. Con- 
tinuing a little farther east, and soon after crossing the stream, the 
slate again gives place to the limerock, and although the second junc- 
tion of the two is not in sight along the road, there can be no doubt 
of their relative position. The dip of all the stratais S. E. Anoth- 
er spot that deserves mention, is a limestone quarry in Pennsylvania, 
along the road from Carlisle to Laudisburg. About a mile north of 
Waggoner’s Gap, where the road crosses the ridge that is there call- 
ed the Blue mountains, (called the North mountains, where our sec- 
tion crosses it, and quite distinct from the Blue ridge,) and close 
Vou. XXVI.—No. 2. 30 
