1914] 



Lawson : Ore Deposition by Meteoric Waters 



241 



bearing - on the question. It is fairly certain that the lower limit of 

 connate waters is the lower limit of unaltered sedimentary rocks; and 

 that may safely be stated to be several miles. The lower limit of 

 meteoric waters in strong rocks is the lower limit of the zone of 

 fracture for such rocks, and that also is several miles. If the exist- 

 ence of the ground-water is not denied, and few will follow Kemp in 

 his efforts in this direction, what happens to it when an intrusive 

 mass invades a sedimentary series dipping toward the intrusion? 

 Does it remain passive, inert ? Does it get heated ? If so, granted 

 the circulation which I have already discussed, does it have activity 

 as a chemical agent? These are some of the questions which Mr. 

 Lindgren must answer before he can claim that his view of the matter 

 is a scientifically established theory. 



MAGMATIC WATER IN EARLY STAGES OF INTRUSION 



Another question which I should like to have answered arises 

 particularly from Dr. Knopf's argument for magmatic deposition, 

 but is also pertinent to many other deposits from alleged magmatic 

 waters occupying fissures in the intrusive itself. What becomes of 

 the magmatic waters and their ore content that escaped in the early 

 stages of intrusion ? If in the later stages of cooling, after the main 

 mass has solidified, after it has been invaded by later intrusions, 

 aplite, porphyry, etc., and there is only a residual magma left, rich 

 in tourmaliniferous "globules of the differentiate from which the ore 

 solutions were derived. ' ' there is an escape of water through the 

 overlying solid igneous rock into its cover, how much more abundant 

 must have been the escape of the waters when the whole mass was 

 molten ! And where are the ores that correspond to this copious 

 escape of water? Why should the escape of the ore-bearing solutions 

 be delayed to the last stages of cooling as Barrell states and as Knopf 

 implies? Further, in this connection, are the pyrogenic ores a late 

 differentiate or an early differentiate of the cooling magma? 



SPURR'S VIEWS 



Spurr's theory of ore deposition at Matehuala is of interest in the 



present discussion. Pie holds : 44 



"... that contact metamorphism began after the intrusive rock had become 

 consolidated, so as to permit of extensive fracture, though under great pressure; 

 that along these fractures the metamorphosing solutions rose from below, and 



■4* Economic Geology, vol. 7, no. 5, 1912, p. 485. 



