RESUME MORRISON FORMATION 443 



structure like joint clay and mainly of gray or pale greenish gray color, 

 with portions which are purple, maroon, or chocolate. Beds of fine 

 grained, light colored sandstones also occur, and in many districts, espe- 

 cially in the lower portion of the formation, there are thin beds of lime- 

 stone in which I have lately discovered a fresh water algse. At various 

 horizons in both the clays and sandstones saurian remains occur, 

 sometimes in vast quantities, and these have been collected extensively 

 at Canyon City, in Morrison, and on the east side of the Black hills. I 

 have recently observed similar bones along the eastern foothills of the 

 Bighorn ranges and along both sides of the Bighorn basin as well. 



The extent of the formation to the eastward, and especially to the 

 northeastward, is not known. Probably^ it would be found in deep bor- 

 ings for some distance northeast of the Black hills, but it is absent in 

 the eastern part of South Dakota, as well as in Nebraska and Kansas. 



LAKOTA-DA KO TA SERIES 



In 1893 Professor Lester Ward discovered that the so-called Dakota 

 sandstone of the Black hills contained not only a Dakota flora, but, in 

 its lower beds, an extensive flora of earlier Cretaceous age. As the 

 Dakota sandstone in its type region is characterized by a distinct Upper 

 Cretaceous flora, it became necessary to restrict the term " Dakota" in 

 the Black hills to the upper sandstone carrying the upper Cretaceous 

 plants. In investigating the stratigraphy of the uplift it was found that 

 the upper sandstone is separated from the lower sandstone, which was 

 designated the Lakota sandstone, by a persistent body of shales, which 

 has been designated the Fuson formation. In tracing these formations 

 northward it was ascertained that the principal plant-bearing horizon in 

 the northern Black hills was in the Fuson formation, and this has yielded 

 a large and beautiful flora of Lower Cretaceous plants, which Professor 

 Ward has described. The tripartite composition of the Dakota group 

 in the Black hills is very distinct throughout the uplift, and apparently 

 it is a widespread feature in adjoining regions. 



Along the eastern base of the Bighorn range there is a sandstone, 

 believed to represent the Lakota, which is overlain by typical clays of 

 the Fuson, but the Dakota sandstone does not appear unless it is repre- 

 sented by some sandy layers among the shales in the base of the next 

 succeeding formation. This same relation is found on the west side of 

 the Bighorn range, and it appears to extend far south in Wyoming. In 

 tracing the beds southward through Wyoming the outcrops of this hori- 

 zon are so discontinuous, owing to the overlaps of Tertiary deposits, that 

 the stratigraphic conditions could not be definitely ascertained. South- 

 east of Casper some suggestion of the regular succession of Lakota, 



LVI— Bull. Geoi,. Soc. Am., Vol. 15, 1903 



