Joseph Barrett. 263 



discusses the changes of mass and volume through meta- 

 morphism, and states, among other things, that the 

 shrinkage in rock of certain compositions may be "from 

 25 to 50 per cent in volume, attended with the evolution 

 of great quantities of gases which at surface pressures 

 and temperatures would amount to several hundred times 

 the volume of the original sediments.' ' 



Metamorphism always remained one of Barrell's fore- 

 most lines of work, and as late as 1914 he wrote a manu- 

 script entitled "Relations of Subjacent Igneous In- 

 vasions to Regional Metamorphism. ' ' It is hoped that 

 this paper may be printed in 1920. 



In the summer of 1900, Barrell was again employed by 

 the U. S. Geological Survey in a two months' recon- 

 naissance of the surface geology of the Deerlodge region 

 of Montana and of the underground geology of Butte. 

 The next year he began, again under the direction of 

 Mr. Weed, a three months ' geological survey of the sur- 

 face and underground geology of the Marysville mining 

 district, Montana. His results were worked out at Yale 

 and published as "Geology of the Marysville Mining 

 District, Montana: a Study of Igneous Intrusions and 

 Contact Metamorphism." This region was one of the 

 noted gold-producing centers of Montana, and the mines 

 were situated around the margins of the irregular 

 Marysville bathylith of quartz diorite, whose surface 

 exposure is from half a mile to one and a half miles 

 broad and two and one-half miles long. This invasion 

 of igneous rock was primarily the cause of the location 

 of the mineral wealth in this district. It is "but 6 miles 

 at its nearest point from the exposed surface of the 

 far greater Boulder bathylith, a granitic mass which is 

 petrographically a quartz monzonite in normal com- 

 position. The Boulder bathylith possesses a general 

 rudely rectangular form, occupying about 60 miles in 

 latitude by about 35 in longitude, and holds within its 

 confines the mining city of Butte, from which for many 

 years past has poured a flood of silver and a quarter 

 of the world's production of copper. Other smaller min- 

 ing centers also lie within this large granitic area, while 

 such important ore deposits as those of Elkhorn and 

 Unionville, south of Helena, have been found about its 

 margin. ' ' 



In regard to the Marysville report, which has now 



