Baltimore and the Ohio River. 227 



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. E. 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 strata is 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 



Vol. XXVL— No. 2. 30 



