1881.1 -•■"-*■ [Stevenson. 



aad marls occur between the gypsums. The opportunities for examina- 

 tion in the Holston region are so limited that one cannot determine 

 whether or not any such variations in activity of the springs occurred 

 there. 



Note. — The map accompanying this memoir is based on the old State 

 map as used by Mr. Boyd in his Resources of Southwest Virginia, but 

 the scale has been changed and a number of alterations have been made. 

 It is still very inaccurate, but no better map is in existence. I have to 

 acknowledge the courtesy of Maj. Powell, Director of the U. S. Geologi- 

 cal Survey, and of Mr. Gannett, Chief Topographer of the Survey, in 

 supplying photographic copies of the unfinished maps of the region. 

 These have afforded real aid in working out the geology at localities where 

 the other map had led me into serious error. 



Some Notes Respecting Metamorphism. By John J. Stevenson, Professor of 

 Geology in the University of the City of New York. 



(Bead before the American Philosophical Society, December 7, ISS4.) 



I have gathered together in this paper a number of notes made from 

 time to time respecting the eflect of certain agencies, which are regarded 

 usually as especially active in inducing metamorphism of rocks. 



Effect of proximity of Metamorphosed Rocks. 



The following section was obtained on Four-mile creek, a stream enter- 

 ing South Park, Colorado, from the west ; the rocks are Siluro-Cambrian : 



1. Limestone, much altered. 



2. Conglomerate and quartzite, imperfectly exposed. 



3. Concealed, with occasional outcroppings of quartzite. 



4. Quartzite. 



5. Limestone, arenaceous, somewhat changed. 



6. Sandstone, unchanged, light gray. 



7. Sandstone, unchanged, shaly partings, dark gray. 



8. Sandstone, slightly changed with layers of unchanged 



shale. 



9. Sandstone, somewhat changed, very micaceous, dark. 



10. Quartzite, mostly white, lines of cleavage distinct. 



11. Granite and gneiss. 



The total thickness of section is not far from 350 feet. A structureless 

 quartzite rests on the Archaean, but above that the degree of change di- 



PROC. AMER. PHILOS. SOC. XXII. 118. U. PRINTED MARCH 6, 1885. 



