DUTTON. 



THE CLOSE OF THE CRETACEOUS. 85 



Directly upon the Trias rests the Jurassic. A wonderful bed of sand- 

 stone 800 to 1,200 feet thick, and very white and sugary iu color repre- 

 sents the principal part of this series. It is a very notable formation 

 because of its remarkable homogeneity, the persistent way in which it 

 preserves its lithological characters through great distances, and the 

 absence of divisional planes of stratification— the mass being solid from 

 top to bottom. But most striking of all is its wonderful cross-bedding, 

 far surpassing in beauty, extent, and systematic character, any similar 

 phenomenon elsewhere, with which I am acquainted. The summit of 

 the Jurassic suddenly changes to calcareous and sandy shales, abound- 

 ing in fossils. This series, as well as the Trias, appears to have been 

 laid down horizontally in shallow waters. 



Next comes the Cretaceous system— a mass of yellow sandstones with 

 clayey and marly shales, aggregating from 4,000 to 5,000 feet thick. In 

 this series we find an abundance of plant remains, many beds of good 

 coal, and much carbonaceous shale. The conditions during the Creta- 

 ceous appear to have been quite similar to those which prevailed in the 

 Appalachian region during the Carboniferous. Perhaps the conditions 

 which attended and rendered possible the accumulation of coal are not 

 sufficiently well understood to enable us to say confidently just what 

 they were, but there seems to be a general agreement that they involved 

 aflat, low, moist country lying almost exactly at mean sea-level, and sub 

 ject to alternate emergence and submergence. No other supposition 

 seems to meet the requirements of the case, or to be capable of explain- 

 ing how a mass of strata could be so accumulated, consisting of alter- 

 nations of thin seams of coal and carbonaceous shale with layers of sand 

 stone containing marine fossils. 



We have now the following remarkable state of affairs. From the 

 close of the Carboniferous to the close of the Cretaceous there is strong 

 evidence that the surface of deposition was always very near to sea- 

 level, sometimes a few feet above it, but for the most part a little below 

 it. And yet in the interval about 9,000 feet of strata accumulated with 

 remarkable uniformity over the entire province, and always in a hori- 

 zontal position. From this it necessarily follows that the mass of mate- 

 rial thus deposited sank or "subsided" at a rate which, in the long run, 

 was exactly or sensibly equal to the rate of deposition. 



At the close of the Cretaceous we find evidence that the long calm 

 which had characterized the action of the physical processes was in- 

 vaded. Some extensive disturbances took place, resulting at some 

 places in the dislocation and flexing of the strata, and the elevation of 

 some portions of the region to considerable altitudes. Erosion at once- 

 attacked the uplifted portio s, and around the borders of the province 

 we find numerous localities, usually not very extensive, which were 

 greatly devastated. At some of these places the entire local Cretaceous 

 series was denuded, and even a portion of the Jurassic; and the Tertiary 

 is seen lying upon the Jurassic and across the beveled edges of the 

 5 G A 



