Baltimore and the Ohio River. 223 
nites, found near Winchester, Va. It was in Virginia, also on the banks 
of Cedar creek, along the line of Frederick and Shenandoah counties, 
that I observed the only remains, that I have been able to discover in 
the graywacke formation of this region. ‘They were two or three va- 
rieties of bivalves, generally so mutilated as to render any attempt to 
determine the species, a very discouraging task. One elongated va- 
riety, bore a slight resemblance to the outline of a butterfly, sufficient- 
ly so, to entitle the locality to the name of “the butterfly rock,” by 
which it is known in the neighborhood. The fact is interesting, 
since it shows that there are other remains, besides those of the trilo- 
bite family, that are probably called petrified butterflies. At the foot 
of the North mountain, west of Hagerstown, we again meet the gray- 
wacke, which continues apparently uninterrupted as far as Hancock. 
Before arriving at that place, the road was for some distance along 
the left bank of the Potomac, where may be seen a fine exhibition 
of red and particolored slates, alternating with each other. A short 
distance west of Hancock, limestone again occurs, but is soon follow- 
ed by arenaceous and conglomerate strata, and these in their turn are 
succeeded by parti-colored slate and red sandstone. On the east face 
of Sideling Hill, a conglomerate appears—on the west side near the 
foot, slate alternating with sandstones. ‘This formation then contin- 
ues a great distance, but varying considerably in external characters. 
The sandstone often assumes the appearance of the calciferous sand- 
rock of Prof. Eaton, as that occurs in Rensselaer Co. N. Y., and 
evidently alternates with a soft argillaceous slate and a coarse con- 
glomerate. The next marked on the section is Town Hill, similar 
in structure to those previously passed. Between this and Polish 
mountain, marked Rugged mountain on the section, the strata exhibit 
some of those contortions and twistings, so often remarked in other 
places, and which will be more particularly noticed, when speaking 
of the direction and dip of the strata. 
This formation continues until reaching the eastern base of Mar- 
tin’s mountain, marked Evit’s mountain, on the section. Here the 
limestone again appears, and seemingly constitutes the mass of this 
mountain, showing itself towards the top and again near its western 
base. On the western declivity, near the top, there are some ap- 
pearances of a white sandstone. The limestone is then succeeded 
by alternating slaty and arenaceous strata, which continue until ar- 
riving within five or six miles of Cumberland. At that point, there 
is a very interesting exhibition of the manner in which the lime is in- 
terposed among the graywacke strata; we see slate supporting a 
