XX LETTER OF TRANSMITTAL, 



the gentlemen furnishing this material we are very greatly indebted. 

 To Mr. James R. Thompson our especial thanks are due for a large 

 amount of gratuitous work, and especially for plats and sections of the 

 majority of the mines of the district, showing the relations of the iron-ore 

 deposits to the surrounding rocks. To the agents, superintendents, and 

 engineers of the mines of the district we are indebted for numberless 

 courtesies. 



Of the manuscript, Chapter I, upon the literature; Chapter II, upon 

 the Basement Complex; Section III of Chapter IV, upon the Clarksburg 

 formation, and Chapter V, upon the igneous rocks, were prepared by W. IS. 

 Bayley. Chapter VI, upon the Republic trough, was prepared by H. L. 

 Smyth. Chapters III and IV, with the excejjtion of Section III of the 

 latter chapter, upon the Algonkian, were prepared by C. R. ^'an Hise, as 

 was also Chapter VII, upon the general geology. 



The drawing for the atlas was done by E. R. Maurer andF. E. Moitow. 

 The beautiful originals for the colored plates were prepared by Mr. J. L. 

 RidgAvay, from ])olished specimens furnished him. They are photographic 

 in their accuracy. 



Very respectfully, your obedient servant, 



C. R. Van Hlse, 



Geologist in Charge. 



Hon. Charles D. Walcott, 



Director United States Geological Survey. 



