BLACK HILLS GEOLOGY. 315 



have resulted from the erosion of the "cement" deposits or au- 

 riferous basal conglomerates of the Cambrian. 



E. Acknowledgements. 



In conclusion the writer takes pleasure in extending his ac- 

 knowledgements for the many courtesies extended to him while 

 in the hills : to Professor F. C. Smith for very kind advice as to 

 field work, localities, etc., and for the published analyses, which 

 have been invaluable in the preparation of this paper, also for 

 many other kindnesses ; to Dr. F. R. Carpenter and Messrs. 

 Chapman, Greenough, A. J. Smith, Johnson, Jackson and Hal- 

 lam for permission to examine mining properties ; and to Dr. 

 W. P. Jenney for courtesies extended. After the completion of 

 field work the writer accompanied Dr. T. A. Jaggar, of the 

 U. S. Geological Survey, in his reconnaissance of Custer Peak, 

 Inyan Kara, Black Butte, Sundance hills, Little Missouri Buttes, 

 Mato Tepee and Warren Peaks. Great care has been taken to 

 make no reference in this paper to these igneous peaks, other 

 than to facts already published, but their study has been an in- 

 valuable aid to a correct understanding of the igneous phenom- 

 ena in the district studied, as also have views suggested by dis- 

 cussion with Dr. Jagger. For many other courtesies the writer 

 is also indebted to Dr. Jagger and Messrs. Tower, Herron and 

 Boutwell of the U. S. Geological Survey. 



In the preparation of the petrography much aid was rendered 

 by the sections of Norwegian types kindly oaned by Dr. Henry 

 S. Washington. 



To Mr. Van Ingen, of Columbia University, and to Messrs. 

 P. v. Irving and J. F. McClelland, the writer is indebted for as- 

 sistance in the preparation of the model of Ragged Top and 

 Elk Mountain and for many other services. 



To Professor Kemp, of Columbia University, the writer espe- 

 cially extends his acknowledgements for advice and assistance 

 during the field work and for kindly criticism and revision 

 throughout the entire preparation of this paper and also for lab- 

 oratory and other facilities for investigation kindly placed at his 

 disposal by the geological department. 



