380 W. M. Fontaine—Mesozoie Strata of Virginia. 
guided or controlled in their courses by variations in the rocks 
across which they flow. ey seem to be steadily deepening 
their channels, which work they “tig continued to perform, 
it would seem, without noteworthy pause since their courses 
were first marked out. 
The absence of any considerable inequality on the surface is — 
well shown along the line of the Chesapeake and Ohio railroad, © 
which runs between Richmond and Gordonsville, for fifty miles, 
directly across the strike of the various strata. In the area now — 
in question the grades of the road are gentle, yet it turns aside 
for no hill, and has only one or two cuts which reach the depth 
into the principal streams. ere are many evidences showing — 
that the level areas between the main streams are remnants of — 
the original plane to which the country was cut down, and that 
the topography is entirely due to the action of the present sys: 
tem of streams in cutting down from this initial plane. 
Thus 
we find in the hill tops, and over the broader levels, certain — 
clays and cobbles which occupy the same horizon always, an 
serve to fix the plane of this old surface. While peculiarities — 
of erosion are shown in the character of some of the strata of 4 
of the deposit of the latest formed beds. 
The condition of the surface of the Azoic rocks is also in- 4 
structive. Those which admit of the formation and retention — 
of smoothed and rounded forms, usually present such appeal: 
ances. This is notably true of the granites and gneisses in the 4 
ort of Richm 
ond. ] 
epth to wns decay has penetrated here is far less than — 
in the southern and southwestern parts of the State. In the lat — 
ter we find strata not lly prone to decay, often decomposed, — 
+e even one hundred — 
feet. This loose matter is suggestive of the way in which some — 
of the later formed Mesozoic beds may have obtained their | 
— and its peculiar arrangement. This will be noticed 4 
and changed to a loose earth, im fifty an 
late: 
ie the area of the Azoic with which we are now concerned 
however, the case is different. We rarely find the rocks decayed _ 
to as much as twenty feet in depth. Very often the suri : 
clays rest on sound rock, or on that which is decompo: 
a few feet below the surface, Again this decay has in nearly mall : 
cases taken place since the erosion above mentioned. We often | 
