104 KEPOET UNITED STATES GEOLOGICAL SURVEY. 



portion must therefore most likely contain a shallow synclinal fold (F). 

 Following' along the Carboniferous outcrop we find the dip of the strata 

 steadily but slowly increasing, until, at the highest point, it reaches 

 about '20°. From the summit of this hill the strata slope off to the 

 northward, rapidly diminishing in dip. In regular succession we find 

 the Permian (c), Triassic (/), Jurassic (<y), and Cretaceous (h) beds. The 

 lull showing the highest outcrop of Carboniferous is located on the 

 central axis of the anticlinal B. It must be remembered that neither of 

 these two sections cut this fold at right angles to its trend, and that in 

 reality, therefore, the inclination of strata is steeper than here repre- 

 sented. 



Section XI begins with beds of the Sweetwater Group, covering the 

 older formations. The first exposure w T e find of older strata consists of 

 Permian beds (e) which appear superimposed upon the massive blue Car- 

 boniferous limestones (d). At the highest point of this latter we notice 

 a slight flexure of the strata. Dipping to the westward originally at an 

 angle of 18° to 20°, they suddenly dip to the east 12° for a short distance, 

 and then resume their former position. Erosion and perhaps breaking 

 of the strata has exposed the Subcarboniferous Group, which we find 

 resting directly against the younger granites. Along this line of section 

 we cut one of the hills composed of this material. It is an isolated one, 

 as is shown by the appearance of Carboniferous beds east of it. A little 

 farther on everything is once more covered by Tertiary deposits. In both 

 sections the Prozoic granites (P) have been indicated as existing, but not 

 yet reaching the surface. 



If we follow the line of the anticlinal (A) we will find it to lead us to 

 the Palaeozoic exposures west of the first masses of metamorphic granite 

 in the Sw 7 eetwater Hills. In a similar manner the second one (JB) points 

 toward the region of disturbance east of Elkhorn Gap. 



At the point first mentioned the Carboniferous strata occupy a very 

 prominent position. They form narrow sharp ridges dipping to the south 

 at an angle of about 70°. Several small canons lead through these 

 ridges into the slopes of the Sweetwater Valley. Here, as well as else- 

 where, the massive blue limestones are entirely conformable with the 

 older beds. So far as could be determined without horizontal measure- 

 ment, the thickness of the beds here amounts to about 1,600 feet. In 

 lithological character the rocks are exactly the same as east of the Wind 

 Eiver Eange. Only for a short distance does this outcrop of Carbonifer- 

 ous beds extend. Probably the beds do not reach sufficiently high up on 

 the northern side to protrude through the Tertiary beds. On the south 

 side they rapidly lose their dip and sink out of sight. 



East of Elkhorn Gap the Carboniferous limestones again appear. An 

 isolated rock, about 200 feet in height first indicates their presence. We 

 found it so steep as to be inaccessible. Strata standing on end have 

 given rise to its formation. From there eastward the limestones follow 

 a narrow line of outcrop. We find th at directly north of this series of Car- 

 boniferous strata a small quantity of granite occurs, winch soon disap- 

 pears, however. Tracing the beds along their strike we observe that 

 the limestones make a sudden bend toward the southeast. At this 

 point a heavier mass of granite jutting up on the north side has caused 

 a complete overturn of the strata, causing an S-shaped fold. The flexure 

 of the strata is such as to produce, on the present surface, a steady dip 

 to the northward. Near the hillside everything is obscured by drift and 

 timber, so that but little can be learned as to the southern continuation 

 of this interesting point. The only indications, indeed, that can be ob- 



