THE TERTIARY GEOLOGY OF THE 
I -.>8 
Im- sc‘cn that the older group ( Mar y land ian) occupies a northwestern area, or that 
adjoining the Eocene ; and tlie newer group (Virginian) the area included between this 
last and that occupied by the post-Pliocene beds to the southeast. 
.\t the time that I prepared the article above referred to on “The Stratigraphical 
Evidence afforded by the Tertiary Fossils of the Peninsula of Maryland,” wherein I 
indicated the existence and positions of the two divisions of the Maryland “ Medial 
'I'ertiary,” I was unaware that Conrad, some forty-five years before, had arrived at 
conclusions approximately identical with my own (although the data supporting his 
position were of a rather fragmentary and not exactly satisfactory character), but which 
he aj)pears to have completely ignored at a later day. Thus in a paper on the 
“ 'I’ertiary Strata of the Atlantic Coast,” published in 1835,* it is stated that between 
the Chesapeake Bay and Potomac River two classes of deposits occur “ besides the 
■ ecpii valent of the London C'lay or Eocene, the first of which, lying most to the westward, 
contjuns fewer recent species than the other, and is well characterized by the gigantic 
Perna maxiUata." Tn my paper already referred to I have also stated that the lower 
or older beds are those which arc characterized by Perna maxillata,^ and it is just 
this species which is likewise largely disseminated through well-known Oligocene and 
older Miocene deposits of Europe. With it occurs Mijlilus iricurva, a large mytiloid 
f()rm, which may be taken to be the representative of the Mytilxis llaidingeri or M. 
Favjasi, forms also distinctive of the European Oligocene and Miocene. 
Virginia. 
The Tcrlimy formntious of this State, for tvhose tlclineation we arc principally 
indebted to the labors of I’rof W. I!. Rogers and Mr. Conrad, pursue a more nearly 
meridional direction than in any of the other States that we have thus far been 
considering. The region occupied by them, designated also as the “Tertiary marl 
mgioii, has hecii dofiliod by Rogers J as embracing “ nearly all that portion of the 
Sti, e inclnded between its eastern boundary, the Chesapeake Bay and the .\tl,ai.tic 
and a hy|mthet,ral line intersecting the principal rivers at their lowest bills. Various 
b, sis of clay and wand, nearly horizontal in position, abounding in fossil shells, and the 
3 wll """■'r'i “"i™"'*’ '’°™ 'h.nracteristic strata of this division of the 
of gvn" mT””"" • 
ate m^ongits oZmalZ^f '°v':.;^“ 
mouth'orrcquta Creek “ K'tetal way with a line passing from the 
Fredericksbur- and th ’ neighborhood (a little outside) of 
inncksbiirg, and thence through Wes, at the junction of the North and Smith 
* of an, I Arts, v.,1. xxViii, p. 106. 
“nsMortng tl.» M. mnUining iW 
