228 The American Geologist. October, 1892 
seems to have departed, and all that remains is to accept, to commemor- 
ate, and to round off the glorious victories of the dead heroes of our 
science. 
But to the patient stratigraphical veteran, who has kept his eyes open 
to discoveries new and old, this lull in the war of geological controversy 
presents itself rather as a grateful Ijreathing time; the more grateful as 
he sees looming rapidly up in front tlie vague outlines of those oncoming 
problems which it will be the duty and the joy of the rising race of young 
geologists to grapple with and to conquer, as their fathers met and van- 
quished the problems of the past. He knows perfectly well that Geol- 
ogy is yet in her merest youth, and that to justify even her very exist- 
ence there can be no rest until the whole earth-crust and all its phenom- 
ena, past, present, and to come, have been subjected to the domain of 
human thought and comprehension. There can be no more finality in 
Geology than in any other science; the discovery of to-day is merely the 
stepping-stone to the discovery of to-morrow; the living theory of to- 
morrow is nourished by the relics of its parent theory of to-daj'. 
Now if we ask what are these formations which constitute the objects 
of study of the stratigraphical geologist, I am afraid that, as in the case 
of the species of the biologist, no two authorities would agree in framing 
precisely the same definition. The original use of the term formation. 
was of necessity lithological, and even now the name is most naturally 
applied to anj^ great sheet of rock which foraas a component member of 
the earth-crust; whether the term be used specifically for a thin homo- 
geneous sheet of rock like the Stonesfield slate, ranging over a few square 
miles; or generically, for a compound sheet of rock, like the Old Red 
Sandstone,many thousands of feet in thickness, but whose collective lith- 
ological characteristics give it an individuality recognizable over the 
breadth of an entire continent. 
When Wei-ner originally discovered that the "formations" of Saxony 
followed each other in a certain recognizable order, a second character- 
istic of a formation became superposed upon the original lithological 
conception — namely, that of determinate "relative position." And 
when William Smith proved that each of the formitions of the English 
Midlands was distinguished by an assemblage of organic remains pecul- 
iar to itself, there became added yet a third criterion — that of the posses- 
sion of "characteristic fossils." 
But these later superposed conceptions of time-succession and life-type 
are far better expressed by dividing the geological formations into zoo- 
logical zones, on the one hand, and grouping them together, on the other 
hand, into chronological systems. For in the experience of every geolo- 
gist he finds his mind instinctively harking back to the bare lithological 
application of the word "formation," and I do not see that any real ad- 
vantage is gained bj^ departing from the primitive use of the term. 
A zone, which may be regarded as the unit oi palteontological succession, 
is marked by the presence of a special fossil, and may include one or 
many subordinate formations. A system, which is, broadly speaking, the 
unit of geological succession, includes many "zones," and often, but not al- 
