Page:Field Notes of Junius Henderson, Notebook 2.pdf/13

a joint plane suddenly changes the course of the stream at right angles for 50 or 75 feet where it flows through vertical walls about 60 ft high and 10 feet apart thus ((drawing in field book)). The last jump of the falls is sheer over a vertical 60 ft. wall formed by a joint plane in the granite just before leaving the granite. The granite lies on both sides of the lateral valley which cuts in from the north at the lower fall. In other words the lateral drainage cuts back into the granite as it does in the region of Boulder Boulder, Colorado, instead of cutting along the contact or into the sedimentaries. This is likely due to the fact that the sedimentaries were laid on a surface of weathered granite. ((at some later date Henderson wrote an emphatic “NO.” at this place in the notebook)). At any rate here the upper part of the granite is weathered, while the lower part is unaffected. If the granite were unweathered there seems no good reason why the cutting should not be in the sedimentaries as they are not particularly resistant, so