1886. } Geology and Paleontology. 1043 
ble for description and illustration, of which the new ones are 
shortly to appear in a Bulletin of the Am. Mus. Natural History, 
with a description of the geology of the region by Professors 
Seely and Brainard—R. P. Whitfield. 
THE VEINS OF SOUTHWESTERN CoLoraADo—It is quite impos- ` 
sible to thoroughly understand the complicated vein-structure of 
the San Juan region without an intimate knowledge of the geo- 
logical history. The details of the stratigraphy are very interest- 
ing, but we cannot stop to review them here. Suffice it to say 
that the succession of the strata, aside from local features of little 
importance for our present purpose, is much the same as in typi- 
cal sections from the Rocky mountains through Wyoming and 
Northern Colorado. 
The real vein-history begins with the close of the Cretaceous 
age, when the great folds took place which afterwards became the 
Seat of volcanic action. I must refer to the previous papers read 
at this meeting of the Association for much of what might 
properly be brought into discussion here, and we may at once 
proceed to a brief description of the veins and their arrange- 
ment. 
In the period of the andesitic outflows the country comprising 
the great San Juan Central area was so situated that the lavas did 
veins. The earliest appear to be those of the La Plata district, 
rated from these two basins, and has been the seat of much sec- 
ondary action, so that the date of its initial stages in vein-forma- 
tion is difficult to determine, but with results similar to those of 
the latest epoch. I am strongly of the opinion that the genesis 
was but little, if any, later than that of the other two sets. 
In the Central San Juan area the complexity is very great, and 
yet the distribution of the veins may be brought into order in a 
_ beautiful system with surprising regularity in the grouping. 
__ There are six radial zones passing out from Red peak (the geyser 
1 Paper read before Section E, A. A. A. S., Buffalo, 1886, 
