218 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
mass of andesite and trachyte was poured out, the remains of which now 
form the Pine Valley mountains and some small hills northwest of 
Toquerville. The Pine Valley lava lies upon the youngest Eocene strata 
in a gentle syncline, which may have been formed either before or after 
the extrusion of the lava, or may be due in part to the bending of the 
strata under the weight of the extruded mass. The smaller andesitic 
hills near Toquerville are either intrusive portions which never reached 
the surface, or stocks of extrusions of which all other traces have now 
been removed. This lava seems to be of nearly the same age as the 
oldest of the successive flows that took place in the region of the High 
Plateaus farther northeast (Dutton, a, pp. 59, 180). Its relation to the 
flexing and folding to be described in the following paragraphs is uncer- 
tain. The fact that the lava covers a surface where little or no trace of 
erosion has been observed makes it seem probable that the volcanic ma- 
terial was extruded before the flexures and folds were completed. The 
latter are of great size, and, if accepted theories are correct, required a 
long period for their completion. Moreover, the flexures are of such a 
nature that the Toquerville region must have been elevated some thou- 
sands of feet above sea-level. At the close of the period of folding, there- 
fore, the sedimentary strata underlying and surrounding the Pine Valley 
mountains must have been exposed to erosion for a considerable length 
of time, unless they were in some way protected. If the lava was not 
extruded till after the completion of the folding, the surface of the 
Eocene strata ought to show considerable erosion. Wherever the con- 
tact of the Eocene and volcanic formations was observed there was no 
evidence of such erosion. The observed localities, however, were so few, 
and the contact was so often covered with talus, that no positive con- 
clusion can be drawn. We may provisionally conclude, then, that this 
oldest lava of our region was extruded before or during the period of 
flexing and folding which we shall now discuss. 
Fiexine AND Fotpine. This folding is a feature peculiar to the area 
immediately around Toquerville. East of a line drawn along the south- 
ern portion of the Hurricane fault and extended northward up the valley 
of Le Verkin creek, the strata are nearly horizontal. Between that line 
and the old shore line of the Mesozoic sea west of the Pine Valley 
mountains the strata are compressed into two synclines and two anticlines 
which culminate in a great overturned fold at Kanarra. North of Kanarra 
the continuation of these plications was not studied ; toward the south 
they gradually die out until, fifteen or twenty miles beyond Toquerville, 
they have greatly broadened and persist only as gentle monoclines dip- 
