12 UNITED STATES GEOLOGICAL SURVEY— TERTIARY FLORA. 



2. Alternate beds of lignite, gray and yellow ferruginous friable 



sandstone, with bluish ash-colored, gray and yellow reddish tinged 

 marls and clays, with three seams, of one or two inches thick, of 

 impure lignite 125 



3. Indurated yellow and ash-colored marls, with three small seams of 



impure lignite, with one thin layer, six inches, of reddish-yellow 

 sandstone 60 



4. Thin veins of eight inches of impure lignite, with numerous fine 



crystals of selenite and masses of petrified wood. 



5. Variegated clays and marls, with much sulphurct of iron and two 



small seams of lignite 33 



6. Impure chocolate liguite, with clay underneath, and large quanti- 



ties of selenitic crystals 2 



7. Light gray and bluish ash-colored indurated sandstone, laminated 



clay and marls, with one or two seams of chocolate-colored im- 

 pure lignites 148 



This section, recording four hundred and twenty-eight feet of strata of 

 the upper part of the Lignitic Measures, is like the part overlying the pro- 

 ductive measures of Canon City coal, as given in my report (1872, p. 324). 

 Here we have a capping of liard sandstone, two hundred feet, over scarcely 

 productive measures, formed by an alternation of beds of soft clay or soap- 

 stone, with an abundance of silicified wood, thin seams of lignite (the outcrop 

 of one near the top indicating two feet), beds of clay hardened and black- 

 ened by carbonaceous matter, etc. Most of the sections of the great Lignitic 

 basin of the north are more generally or mostly of the upper strata. The 

 thickness of its lower coal-measures is, however, locally very great; for Prof. 

 Hayden, in his Report (1874, p. 21), says that the lower brackish-water beds 

 arc more than two hundred feet in thickness, and that those that are purely 

 fresh-water must reach an aggregate thickness of tliree thousand to five 

 thousand feet, with from twenty to thirty beds or seams of lignite (not including 

 thin seams of an inch or two, which are very numerous). The lignite beds 

 average from six inches to ten feet in thickness. 



Though the di.>itril)ution of the strata of the southern basin has been 

 distinctly and specially exposed in numerous reports of Dr. Hayden and his 

 assistants, as T have myself carefully surveyed a large part of it — that extend- 



