Stone — Granitic Breccias of the Cripple Greek Region. 23 



combed and more or less decomposed. We therefore cannot 

 admit that the dike iissures were either opened or enlarged by 

 the melting of the older rock and its absorption into the liquid 

 lava. 



2. The case of a dike whose upper extremity moved after 

 solidification. Elevation 10,120 feet. 



About a mile west of Grillett is a phonolite dike, a mile or 

 more in length. It everywhere pitches to the west, but on the 

 Ed. Wolcott claim, a few hundred feet northeast of the Lin- 

 coln mine, it dips less than the average, about 20° below the 

 horizontal. In one of the shafts at a depth of about 30 feet, 

 this dike is seen to be three feet thick and to be frozen fast to 

 the adjacent granite, proving that at this depth there has been 

 no motion of the dike since solidification. The dike is here 

 crossed by cracks in various directions, but the sides of the 

 blocks of fracture are not slickened. Near 50 feet eastward is 

 another shaft which cuts through nine feet or so of somewhat 

 shattered granite, there penetrates a bed of gravel consisting 

 of broken phonolite, and then enters the granite again. The 

 gravel bed dips toward the dike in the more western shaft and 

 evidently is the same dike, but in a broken condition. Most 

 of the pieces of phonolite are subangular in outline, and all are 

 more or less smoothed and rounded at the angles of fracture, 

 but some are quite round and pebble-like. 



The interpretation is unmistakable. The front end of the 

 dike solidified while the lower portion still remained liquid. 

 Probably this happened during a pause in the advance of the 

 dike. Whenever the dike moved after solidification, the solid 

 lava would be broken up and the pieces were slickened by their 

 grinding against each other and the uneven granite walls of the 

 dike. The workings do not show the length of the portion of 

 the dike that was pushed forward after solidification. It could 

 not have been more -than about 50 feet, that is, the part now 

 beneath the surface of the granite. All this happened beneath 

 the surface of the granite, where there can be no suspicion of 

 ice action or of either surface or subterranean waters to smooth 

 the stones in question. Indeed it is not certain that the dike 

 here reached the surface, though it did for most of its course 

 for a mile or more, and the outcrop is marked by low ridges of 

 phonolite blocks having their original shapes of fracture some- 

 what modified by their being polished and a little rounded at 

 the angles. On the hill south of the Lincoln mine these 

 smoothed blocks form a crooked double ridge enclosing a hol- 

 low between the two ridges. There is thus the most ample 

 proof that the frontal portion of the dike continued its upward 

 motion after solidification. I have not examined the broken 

 portion of the dike with the compound microscope, but under 



