GEOLOGICAL SUEVEY OF THE TEREITOEIES. 



109 



The streams that form the headwaters of the Gallatin River have 

 CAit profoundly into the mountain- ^ 

 rauges, exposing their structure in i* 

 the most beautiful manner. The g 

 first of the caiions to which I will | 

 refer is Spring or Rock Caiion. This g 

 cauon forms a most interesting sub- | 

 ject of study, and will answer ad- g 

 mirably as a type of the others. It ° 

 is a V-shaped chasm, cut through S 

 the end of an anticlinal range by ^ 

 the stream. The trend of this range s; 

 is northwest and southeast. The k 

 first thing that attracts our atten- i 

 tion after we are fairly inside the § 

 caiion is the occurrence, on the left- ® 

 hand side of the creek, of an arch S 

 that crosses the road, and, describ- -o 

 ing a semicircle on the hill, again | 

 crosses the road at the upper end g: 

 of the caiion. (Fig. 26.) The first i? 

 prominent bed we meet is a layer |; 

 of coarse, gray calcareous sand- ^ 

 stone, containing fragments of fos- g 

 sils. Proceeding up the caiion we | 

 find the center of the arch is occu- p 

 pied by masses of Carboniferous 3- 

 limestone, which tower far above B. 

 the creek, giving a most pictur- | 

 esq^ue appearance to the canon, g 

 Still farther along we come to the f 

 other extremity of the arch and §. 

 find the same layer that we saw at | 

 the opposite end. Following this "^ 

 layer at the western end of the h 

 canon, that nearest Fort Ellis, we h 

 find the dip at the bed of the creek % 

 to be south 45<^ west; angle, 30O-40o. ^ 

 Farther along we find it to be south §■ 

 80° west, the angle remaining about ^ 

 the same. Still higher up on the p 

 ridge it is north 50° west; angle, 9 

 15°-25°; and when we reach the ^ 

 highest point on the ridge it dips I 

 due north at an angle of about 25°. y 

 Taking this same layer again at the w 

 level of the creek, this time at the =: 

 eastern end of the caiion, we find 1 

 the dip to be in the same direction, g 

 although the angle is greater. As "i 

 we go toward the south it ap- m 

 proaches more and more to the ver- '^ 

 tical, until the dip becomes north- |. 

 east and the range therefore be- I 

 comes a true anticlinal. The read- ? 

 ing just above the creek on the ' 

 northern side gives a dip of south 45° west ; angle, 70°. As we follow 



