X CONTENTS. 



Chapter VI. — Economic geology, by George H. Eldridge — Continued. Page. 

 Section I. — Coal — Continued. 

 Coal areas— Continued. 



Boulder coal field — Continued. 

 Coal Creek syucline — -Continued. 



The Mitchell district 366 



The Canfield-Erie district - : n l T" 



The area cast of Coal Creek 368 



White Rock area 371 



Other mine localities of the lower Laramie coal measures, in the vicinity of the 



I leiiver Basin 371 



The Sera 1 1 ton coal field of the upper Laramie 373 



The eoal 375 



Chemical analyses of individual samples 375 



Chemical analyses arranged according to mining districts 376 



Peculiarities presented in foregoing table 378 



( reneral discussion 381 



Classification of the coals 385 



Special samples of coal 386 



Section II.— Clays 387 



Fire clay 387 



Clay for manufacture of building materials 391 



Seri ion III.— Building stones 392 



Inn oil net ion 392 



Silurian building stones 393 



Triassic building stones 393 



Stone for superstructures 394 



Stone for foundations, lower courses of buildings, flagging, curbing, and paving 394 



Cretaceous building stones 397 



I he 1 astle Rock building stone (rhyolitic tuff) 399 



< >t her building stones 400 



Product 400 



Section IV. — Artesian wells 101 



History of development for Colorado 401 



Early attempts 401 



Activity in the Denver Basin 402 



Wells in interniontaiie valleys 404 



Artesian eomlit ions of the 1 lenver Basin 404 



Conditions of composition and stratigraphy in the Denver Basin 406 



Water-bearing horizons 406 



An upper confining stratum 408 



Conditions of structure in the 1 tenver Basin 410 



Hydrography •_ 413 



Rainfall 413 



I Hscharge of streams ( run-off) 413 



Evaporation 116 



Water available for absorption 417 



