XIV LETTEK OF TEANSMITTAL. 



Geological Survey and had prepared a systematic ri-jiort upon this ]3art 

 of it. He was thus able to direct the more detailed examination of the 

 whole area so that no loss of tin!e should occur. The jdan of the work 

 and of the present book is very largely his. 



The descriptions of the formations and thin sections are, for special 

 reasons, given in greater detail than is intended with any subsequent area. 

 This is the first of the iron-producing districts of lake Superior in which the 

 geology has been worked out in detail, and the fundamental conclusions 

 reached are in opposition to those expressed by some geologists; so that it 

 was tliought necessary to make the facts fully accessible to those who 

 desire to have them. The succession of formations is so clear also that it 

 is believed that the results contained in this report will serve as a key to 

 unlock, in a measure, the more complicated geological structure of the 

 adjacent iron-producing districts. In order to enable the general reader to 

 avoid details, the descriptions of particular rock exposures and their thin 

 sections for each of the formations are placed together in small type. 



To Mr. J. Parke Channing our especial thanks are due for a large 

 amount of gratuitous work, and in particidar for his detailed examination 

 and drawings of maiiy of the mines, and for the facts ct)ntained as to tlie 

 structural relations between the dike rocks and ore bodies. As mining 

 inspector of Gogebic county, he resided in the district and has from time 

 to time given us the results of the latest developments. Mr. .T. M. Long- 

 year, of Marquette, Michigaii, lias also given us niucli assistance, including 

 access to his very large collection <>\' spcciiiiens of the Gogebic end (»f the 

 range, made as the agent of the Lake Superior ;nid Portage Ship Canal 

 Company. To Mr. B. N. Wliite and Mr. Charles Oley, woodsmen, we are 

 indebted for all the assistance which could be given by skilled men some- 

 what familiar with the district. To numerous miners and mine superin- 

 tendents we are indebted for ni;iuy courtesies. AVitli a few exceptions, 

 information with reference to mining properties has been freely granted to 

 us by all. 



The original design was to publish the whole book as a joint produc- 

 tion, but the deatli of Prof Irving occurred in the midst of the preparation 

 of the volume, so that nuich of it has wholly devolved upon me; conse- 



