242 ANNUAL OF SCIENTIFIC DISCOVERY. 



so as to strike north and south, and the other one so as to trend 

 east and west ; but this is quite seldom, and never occurs unless 

 there has been some marked disturbance of the rocks. There 

 are, however, a few lodes which are called " east and west 

 lodes," and some " north and south." A few have a strike north- 

 west and south-east, but are generally very narrow and break off 

 from the north-east and south-west lodes, are very rich for a time, 

 and then pinch out. It would seem, therefore, quite possible that 

 the north-east and south-west veins took the lines of cleavage in 

 that direction as lines of greatest weakness, and that the north- 

 west and south-east lines cross the other set, and that a portion of 

 the mineral matter might accumulate in that cleavage fissure. I 

 merely throw out this as a hint at this time which I wish to 

 follow out in my future studies. I am inclined to believe that the 

 problem of the history of the Rocky Mountain ranges is closely 

 connected with these two great sets of cleavage lines. As I have 

 before stated, my own observations point to the conclusion that 

 the general strike of the metamorphic ranges of mountains is 

 north-west and south-east, and that the eruptive trend north-east 

 and south-west. The dikes, that sometimes extend long distances 

 across the plains, in all cases trend north-east and south-west, or, 

 occasionally, east and west. The purely eruptive ranges of the 

 northern portion of the San Luis Valley seem to be composed of 

 a series of minor ranges en echelon with a trend north-east and 

 south-west. But as soon as this range joins on to a range with a 

 metamorphic or granitic nucleus, the trend changes around to 

 north-west and south-east. Many of the ranges have a nucleus of 

 metamorphic rocks, though the central and highest portions may 

 be composed of eruptive peaks and ridges. In this case the 

 igneous material is thrust up in lines of the same direction as the 

 trend. It becomes, therefore, evident that all the operations of 

 the eruptive forces were an event subsequent to the elevation of 

 the metamorphic nucleus. This is shown in hundreds of instances 

 in Colorado and New Mexico, where the eruptive material is 

 oftentimes forced out over the metamorphic rocks, concealing 

 them over large areas. 



All over the mining districts are well-marked anticlinal, syn- 

 clinal, and what I have called monocliual valleys. Nearly all the 

 little streams flow a portion or all their way through these mono- 

 clinal valleys or rii'ts. In most cases the streams pass along 

 these rifts from source to mouth, but occasionally one bursts through 

 the upheaved ridges at right angles, and resumes its course again 

 in some monoclinal opening. 



In these valleys are oftentimes accumulated immense deposits 

 of modern drift. The upper side of this drift deposit is fine sand, 

 but the materials grow coarser as we descend, until, at the lower 

 side, there are immense irregular or partially worn masses of 

 granite. On the sides of the valley the rocks are often much 

 smoothed and grooved as if by floating masses of ice. We 

 assume the position, of which there is most ample evidence all 

 over the Rocky Mountain region, that at a comparatively modern 

 geological period the temperature was very much lower than at 



