52 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



could have been clearly made out, since they have been subjected not only 

 to the dynamic movements which brought about the present elevation of 

 the range, but, no doubt, to many previous movements of which no record 

 now remains. As a consequence they are found to be contorted, fissured 

 and reconsolidated, and fissured again, and this action seems to have been 

 more intense the further one goes from the original surface, or rather from 

 that which was the surface at the commencement of Paleozoic deposition. 

 In general, it may be said that the pegmatites are the latest formations in 

 the Archean proper, leaving out of consideration, of course, the later erup- 

 tives (porphyries, porphyrites, and diorites) and that gneiss must certainly 

 have formed part of the original undisturbed mass, while of the granites 

 proper some were earlier and some later, but all previous to the pegmatite. 



On the accompanying plate (Plate IV) are reproduced a few hasty 

 field-sketches of occurrences in which the different varieties of rock are 

 found so intimately interlaced as to afford some idea of their relations and 

 of the difficulty of tracing a sequence in their formation. 



In Fig. 1, it is seen (1) that across the original gneiss a small feldspar 

 vein has been formed, probably the filling of a small fissure or crack result- 

 ing from dynamic movement; (2) that the fine-grained and probably erup- 

 tive granite has been intruded in tongue-like masses into the gneiss after 

 the formation of this first vein; (3) that after consolidation the mass has 

 again been shattered, a great fissure formed and filled by a coarser-grained 

 granite, which surrounded fragments of gneiss a'nd earlier granite alike ; this 

 fissuring was accompanied by a certain amount of faulting; (4) a second 

 opening on the wall of this fissure has been made and filled with pegmatite. 



In Fig. 3, again, fragments of gneiss are found in a mass of fine-grained 

 granite, in such position as to show that the latter must undoubtedly have 

 been a more or less fluid mass, which traversed the gneiss and caught up 

 included fragments of it in its passage. 



In Fig. 2, on the other hand, this granite is seen to have been sub- 

 jected to at least two movements; as a result of the first, narrow feldspar 

 veins have been formed across its mass, and again, by the second, these, to- 

 gether with the inclosing granite, have been successively opened along the 

 same fissure to admit the formation in fissures thus made of pegmatite 



