BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 32, pp. 395-416, PLS. 2-6 DECEMBER 1, 1921 



ON METAMORPHISM IN METEORITES^ 



BY GEORGE P. MERRILL 



{Presented by title before the Society December 29, 1920) 



CONTENTS 



Page 



Introductory statement 395 



Discordant nature of opinions relative to original and secondary structure 396 



Structures common to unaltered spherulitic forms 399 



Structures common to crystalline spherulitic forms 400 



Structures common to crystalline forms 401 



Structures common to wliite, gray, and intermediate forms 401 



Causes of variation in structure 402 



Agencies of metamorphism 405 



Summary of conclusions 413 



Explanation of plates 415 



Introductory Statement 



For some years there has been a growing feeling among those who have 

 given the subject consideration, that the peculiar structures found in 

 many meteoric stones are due not to hasty crystallization from a molten 

 magma, as has been argued by some, but rather to an origin through the 

 metamorphism of tuffaceous materials. Statements to this effect, how- 

 ever, with the exception of those of Befwerth, Linck, Eenard, Tschermak, 

 and Wahl, noted below, have been given largely as matters of opinion, 

 without a systematic presentation of the evidence pro and con. It is pro- 

 posed here to bring together for record some of the more important data 

 bearing on the subject and supplement them by results gained through 

 my own studies. 



To one at all versed in the study of meteorites, it is not necessary to 

 remark that the existing structural features, both those of the constituent 

 minerals and the stones as a whole, render it more difficult to trace with 

 "nnal certainty changes which may be due to metamorphism than is the 



* Manuscript received by the Secretary of the Society June 2, 1921, 

 This paper was read before the National Academy of Sciences April 25, 1021. It is 

 printed with the permission of the Secretary of the Smithsonian Institution. 



(395) 



