MAKvixE.] GEOLOGY NONCONFORMITY AT HOT SPRINGS. J69 



As the Hot Spring fold gradually rose, the edges of the Cretaceous and 

 of the breccia must have been eroded back to where the latter was 

 nearly horizontal, before the lignltic beds were deposited upon their 

 edges. This state of things is shown in the following diagram, Fig. 15, 

 in the western end of wjiich, near the springs, the dips are as they now 

 exist, indicating the flexure to be as shown by the dotted lines: 



Since the Eocene beds in and on the west side of the breccia synclinal 

 are inclined eastward with the breccia slightly, some movement must 

 also have taken place since their deposition. This probably occurred at 

 the same time that the east side of the synclinal was upturned, which 

 obviously took place after the lignitic period, for upon this side the lig- 

 nitic beds are everywhere upturned steeply with the breccia and Creta- 

 ceous below. This was at the great mountain-forming period, when the 

 greatest recent folding of the Rockies occurred. It was at this time, 

 probably, that the rocks of No. 5, as shown in the hog-back ridge above 

 the Hot Springs, were inclined from a flatter dip to their present dip of 

 25° or 30°, while this later fold seems to be also indicated by a very 

 gentle anticlinal appearance beneath White Face Mountain. 



Let us turn to the evidence of this unconformability between the Cre- 

 taceous and lignitic south of the Grand Elver. The Grand flovv's close 

 to the southeast base of Mount Eross. On the south side of the river 

 there is no corresi)onding eminence, the tributary from that side of the 

 stream occupying a rather flat and open valley. The edges of the 

 breccia ridge line this valley on the northeast, and following them along 

 they are found to swing eastward and then northward, joining the 

 southward extension of the upper breccia ridge of the Grand. In other 

 words, the breccia outcrop is continuous throughout, showing the fold 

 to be a synclinal, with its axis dipping northwest, thus exposing the 

 edges of the bed in the form of a great spoon, with the point directed 

 southeastward, and filled with the lignitic beds in terrace form, the 

 eastern side being bent up much steeper than the western one. The 

 map shows this clearly, while it is far better presented pictorially in the 

 accompanying sketch. Fig. IG, made by Mr. Holmes from points upon 

 Mount Bross. The terraces and breccia palisades, with the many pic- 

 turesque accessories of the region, as seen from this point, form a very 

 interesting as well as beautiful view. 



Thus the lignitic beds do not lap over and cover the edges of the 

 breccia south of the river as they do between Mount Bross and White 

 Face south of it. South of the valley, and opposed to the breccia i^alis- 

 ades, however, the lignitic again occurs, the edges of the nearly horizon- 

 tal beds appearing on the rather steep slopes leading up to station LIV. 

 From this point the spurs of the LIV ridge extend westward toward 

 the granite canon below the Hot Springs, showing very indistinct terrace- 

 forms, but sufficient to indicate a very nearly horizontal bedding 

 throughout. In the valley, at their northern base, and southeast of the 

 springs, however, are two or three ridges of cretaceous sandstones out- 

 cropping from the otherwise soil-covered valley. These dip eastward 

 toward the breccia ridge, and trend toward the lignitic mass on the south 

 in such a way, and approach so near to it, that, though no direct con- 

 tact was seen, they must pass unconformably beneath it, (see sketch.) 

 Two or three miles west of these ridges, and nearly a mile west of where 

 the quartzites of No. 1 would appear to pass the lignitic beds, and but 

 little south of the canon, the western extension of the LIV mass shows 

 the characteristic coarse brown sandstones of the lignitic in a precipice 

 two or three hundred feet high, dipping 10° or 12° to the south. These 

 sandstones must here rest directly on the granite. 



