1S75.] ^^J- [Stevenson. 



CONCLUSIONS. 



As the Lower Lignitic Group underlies a great mass of strata, contain- 

 ing abundance of Cretaceous species, its geological relations have long been 

 regarded as definitely settled. For precisely the same reason there is no 

 longer room for dispute respecting the Vancouver beds. 



In the matter of the Great Lignitic Group the evidence is not so easily 

 obtained as in the other cases, nor, when obtained, is it so absolutely 

 convincing as to stop all discussion. Looking over the facts already 

 given, one finds 



First, That the Cretaceous, No. 5, and the Great Lignite Group are 

 everywhere comformable to each other, and that the latter is conformable 

 within itself and unconformable to the fully recognized Tertiaries above it. 

 In an area of many thousands of square miles, which has been closely ex- 

 amined in almost all its parts, only two instances of unconformability be- 

 tween the groups have been recorded, both of which are very local, while 

 one of them is, to say the least, of uncertain existence. 



Secondly, That from the beginning of Cretaceous, No. 5, to the close 

 of the Great Lignite Group, there was no change in the general condi- 

 tions, which would be of more than merely epochal value. The Upper 

 Cretaceous (No. 5), is a rusty yellow sandstone, usually concretionary 

 when compact, which passes upward imperceptibly into the rusty-yellow 

 sandstones at the base of the Lignitic Group, themsel ves more or less con- 

 cretionary. Ordinarily the gradation from one to the other is so perfect 

 that they cannot be separated. At few localities indeed is it possible to 

 define any line of separation. In Colorado, the fossils of No. 5 are 

 usually absent from the lower sandstones, so that the Lignitic Group 

 appears to rest directly upon the shales of the Middle Cretaceous. The 

 only fossils characteristic of No. 5, ever obtained from Colorado, were 

 procured from rocks, which are most probably among the very highest 

 strata of the Lignitic series. 



The variation in character of the strata above the fucoidal sandstone, 

 giving us shales, sandstones, coal beds, and local limestones, is hardly 

 sufficient to be of even epochal value. The marine conditions remained 

 the same, for the fucoid Halymenites major passes through the series, and 

 the land conditions could have undergone but little change, for of the 

 plants, whose leaves occur in the great sandstone, many occur higher up 

 in the group. The sandstones themselves exhibit a very remarkable re- 

 semblance to each other. The changes in structure are no greater or 

 more abrupt than those in the Coal Measures. It is quite evident that 

 the relations of the great sandstone (in which I include also that portion 

 termed Cretaceous, No. 5), to the main series of lignites, is precisely the 

 same with that held by the Conglomerate to the Coal Measures. In each 

 case the underlying mass contains thin beds of coal, and is part of the whole 

 series, distinct yet not separate. No one would think of placing the 

 Conglomerate and the Coal Measures in different periods, much less in 

 different ages. 



A. p. s. — VOL. XIV. 3i 



