232 The American Geologist. October, isos 
Draw a section of the surface of the lithosphere along a great circle in 
any direction, the rule remains always the same; crest and trough, hight 
and hollow, succeed each other in endless sequence, of every gradation 
of size, of every degree of complexity. Sometimes the ridges are conti- 
nental, like those of the Americas; sometimes orographic, like those of 
the Himalaya; sometimes they are local, like those of the English Weald. 
But so long as we do not descend to minor details we find that every line 
drawn across the earth's surface at the present day rises and falls like 
the imaginary line drawn across the surface of the waves of the ocean. 
No rise of that line occurs without its complementary depression; the 
two always go together, and must, of necessity, be considered together. 
Each pair constitutes one of those geogrcqMcal units of form of which 
every continuous direct line carried over the surface of the lithosphere 
of our globe is made up. This unit is always made up of an arch-like 
rise and a treugh-like depression, which shade into each other along a 
middle line of contrary curvature. It resembles the letter S or Ho- 
garth's line of beauty, and is clearly similar in form to the tjqjical wave 
of the physicist. Here, then, we reach a very simple and natural con- 
clusion, viz.: the surface of the earth-crust of the present daj^ resembles 
that of a series of crust-waves of different lengths and different ampli- 
tudes, more or less irregular and complex, it is true, but everj^where 
alternately rising and falling in symmetrical halves like the waves of 
the sea. 
Now this rolling wave-like earth-surface is formed of the outcropping 
edges of the rock formations which are the special objects of study of 
the stratigraphical geologist. If, therefore, the physiognomy of the face 
of our globe is any real index of the character of the personality of the 
earth-crust beneath it, these collective geographical features should be 
precisely those which answer to the collective structural characters of 
the geological formations. 
In the earlier days of geology one of the first points recognized by 
our stratigraphists was the fact that the formations were successive 
lithological sheets, whose truncated outcropping edges formed the pres- 
ent surface of the land, and that these sheets lay inclined at an angle 
one over the other, or as William Smith quaintly expressed it, like a 
tilted "pile of slices of bread and butter." But as discovery progressed 
the explanation of this arrangement soon became evident. The forma- 
tions revealed themselves as a series of what had originally been de- 
posited as horizontal sheets, lying in regular order one over the other, 
but which had been subsequently bent up into alternating arches and 
troughs (^'. e. the anticlines and synclines of the geologist). Their vis- 
ible parts, which now constitute the surface of our habitable lands, were 
simply those parts of the formations which are cut by the irregular 
plane of the present earth's surface. All those parts of the great arches 
and troughs formerly occurring above that plane have been removed by 
denudation; all those parts below that plane lie buried still, o«t of sight 
within the solid earth-crust. 
Although in every geological section of sufficient extent it was seen 
