76 THE GEOLOGY OP MINNESOTA. 



[Th<.> crystalline rooks. 



This work is based on the examination of about 3,000 microscopical thin sections. 

 They were made by different assistants, and by M. C. Marchand, preparateur to the 

 Museum d'Histoire Naturelle, Paris. The first thin section of rock ever made at the 

 University of Minnesota was ground and mounted by the senior author of this in 

 1879, by the use of a lithologist's lathe procured of Prof. A. A. Julien, of New York.* 

 Since that many other sections have been made on the same lathe by Messrs. Herrick, 

 Terry, Oestlund, Wood, Meeds and Ogaard. It is run by the water-pressure derived 

 from the city waterworks of Minneapolis; and from time to time some results of 

 microscopical study have been published. We have had available as aids all the litera- 

 ture which has been published in this country bearing on the subjects investigated, 

 and much of that of Europe. Our microscopes are, besides the original Toll micro- 

 scope purchased in 1879 and specially remodeled for petrography under the direction 

 of Prof. Julien, an Acme lithologist's microscope made at Lancaster, Pennsylvania, 

 and refitted by Bausch and Lomb, and a Nachet Grand Modele with some recent 

 attachments. 



Finally, acknowledgments are due to Prof. A. Lacroix, of the Museum d'Histoire 

 Naturelle, Paris, for assistance received during the year 1895, which was spent by 

 the senior author at work in his laboratory on a series of Minnesota rocks. Many of 

 the important and also of the special determinations have had the sanction of his 

 approval. A second visit for the same purpose was made in 1898, and many sugges- 

 tions were received again from Prof. Lacroix. We wish to record a lively apprecia- 

 tion of the enlightened generosity of the French republic in supporting at Paris such 

 institutions as the Museum d'Histoire Naturelle, offered free to all naturalists for 

 the research which they wish to carry on. 



LIST OF PUBLICATIONS TO WHICH REFERENCE HAS FREQUENTLY BEEN MADE, BEARING ON THE 

 PETROGRAPHY OF MINNESOTA, ARRANGED CHRONOLOGICALLY. 



1871. J. H. KLOOS : Zeit. d. deutscb. geol. Gesell, xxiii, page 417 (with a map). Translation in the 

 the tenth Minnesota Report. 



1871. R. PUMPELLY : The Paragenesis and Derivation of Copper and its Associates on Lake Superior, 

 American Journal of Science (3), vol. ii, September, October and November. 



1877. A. STRENG and J. H. KLOOS : Ueber die Krystallinischen Gesteine von Minnesota in Nord-Amerika. 

 Neues Jahrbuch fiir Mineralogie, 1877 [translation in the Eleventh Minnesota Report]. 



1878. R. PUMPELLY : Metasomatic Development of the Copper-Bearing Rocks of Lake Superior. Pro- 

 ceedings American Academy of Arts and Sciences, vol. xiii. 



1879-1895. Annual Rejwrts of the Minnesota Survey. 



1880. R. PUMPELLY: Lithologyof the Keweena wan or Copper-Bearing Rocks. Geology of Wisconsin, vol. 

 iii, pages 27-49. 



1882. R. D. IRVING : Microscopical Examination of the Archean Rocks of the Upper Flambeau Valley. 

 Geology of Wisconsin, vol. iv (1873-1879). 



1883. R. D. IRVING : The Lithology of Wisconsin. Geology of Wisconsin, vol. i, pages 310-361. 



1883. R. D. IRVING : On the Paramorphic Origin of the Hornblende of the Crystalline Rocks of the 

 Northwestern States. American Journal of Science (3), xxvi, page 27; xxvii, page 130: xxviii, page 464. 



1883. R. D. IRVING: The Copper- Bearing Rocks of Lake Superior, Monograph No. V, U. S. Geol. 

 Survey; Third Annual Report U. S. Geol. Survey, pages 89-188. American Journal of Science (3), vol. xxix, 

 page 258. 



'Eighth Annual Report, p. 10, 1879. 



