MUSEUM OF COMPARATIVE ZOOLOGY. 65 
Below the cliff, a few outcrops of sandstone or conglomerate may be 
found. These data for a cross-section are less complete than those col- 
lected on the previous day, but they suffice for a rough diagram added 
in the margin of Fig. 3. 
On the supposition that the whole valley consists of an unbroken 
monocline, the two sections now constructed can be placed in their 
proper relative positions by means of a map, which would result in show- 
ing that the second belongs about four and a half miles westward across 
the strike from the first, and therefore its beds stand about five thou- 
~ sand feet below those of Lamentation. But, if not already noticed, 
attention will soon be called to the similarity between the two sections ; 
and the question then arises, how can this be best explained. It may 
be the result of similar processes repeated in a given order, whereby 
similar sequences of beds were deposited at different times; or it may 
be the result of one or more strike-faults, by which portions of a single 
sequence of beds are brought to the surface in different places. It re- 
mains to decide between these two alternatives. 
A general consideration of the problem will make it evident that the 
explanation by repetition of similar processes becomes less likely, and 
that the explanation by faulting becomes more likely, with the increase 
in the number of beds in the repeated series; with the lack of genetic 
relation among the members of the repeated series; and with the in- 
crease in the number of times that such repetitions occur. It should 
also be noted that the two explanations are not mutually inconsistent ; 
both might apply in a single field. . 
The drift covers so much of the surface that detailed sections cannot 
be constructed. The stratified beds are, on the whole, so much alike, 
that the precise identification of equivalent beds by agreement in com- 
position is impossible. While it may yet be found that fossils will serve 
as a guide to the recurrence of repeated outcrops, this means of identifi- 
cation cannot at the present time be applied in the region we are exam- 
ining. All that can be done is to make the best of imperfect evidence. 
We may first examine the argument based on the number of members 
in the repeated series. The completed sequence of visible beds is: con- 
glomerate and sandstone; trap of moderate thickness; thin limestone ; 
shaly sandstone ; heavy sheet of trap; more shaly sandstone; a thin- 
ner sheet of trap; and, finally, more sandstone. It may be conceivable 
that this sequence of beds was independently made at two different 
times; but it is not at all likely that so considerable an agreement 
should be the result of the accidental repetition of a sequence of deposits. 
VOL. XVI. — NO. 4, 5 
