222 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
turbed must have been highly folded, those at moderate depths must 
have been gently flexed, and those near the surface must have been 
faulted. None of the deep-seated strata are to-day exposed. The strata 
in which the Jurassic and early Tertiary plications are now visible at the 
surface were at the time of folding buried beneath a moderate depth of 
overlying strata, and usually show gentle folds formed without faulting. 
Those layers in which the later movements are shown were relatively 
close to the surface, and are almost always faulted without bending, 
since they were free to break as soon as they were strained. The line 
of greatest displacement seems to have shifted eastward from the Basin 
Range province in Jurassic times to the western margin of the Plateau 
Province in the early Tertiary, and to the centre of this latter province 
in the middle Tertiary. In the most recent uplift it has shifted back 
toward the borderland between the two provinces. 
Resuttine TopocrapHy. At the end of the period of folding and 
flexing, which was probably completed early in the Miocene, there must 
have been atime of quiet of uncertain duration, the turning-point between 
the movements which we have been discussing and those of an opposite 
character which followed. Let us pause long enough to get in mind the 
condition of the country at this time in so far as we are able to restore 
them. As we have seen, the region around Toquerville had been thrown 
into a series of close folds which toward the south fade into eastward 
dipping monoclines. Farther east there were a number of similar mono- 
clines (Dutton, ¢, pp. 41, 115, 128, 185). On the basis of these facts 
we can to a certain extent reconstruct the topography of the country, 
although erosion, the amount of which we cannot measure, must have 
greatly changed it from the simple forms due merely to the original 
rock structure. To the west lay the elevated and probably maturely 
dissected “old land” which is now the Basin Range province. Last of 
this was an extensive area of recently uplifted sediments, a raised and 
more or less folded and flexed coastal plain. Neglecting for the moment 
the effects of erosion, the western part of this consisted of a narrow belt 
of closely folded mountains near Toquerville not far from the old sea 
margin. The greater part of the coastal plain, however, consisted of a 
series of broad initial terraces which descended gradually eastward toward 
the distant sea, and of which the steep portions were formed by the 
gently dipping monoclines. To what extent the strata had been dis- 
sected and removed by erosion we cannot say, nor do we know the 
course of the streams. Ifthe drainage was consequent, as would in all 
