GEOLOGY AND PALEONTOLOGY. ISI 
INVERTEBRATES AND RECENT INVESTIGATIONS. 
Another phase of the history of the Dakota group remains to be considered, and 
that but briefly. It is the question of invertebrates. From almost the first men- 
tion of the sandstone by Meek and Hayden the paucity of animal remains was con- 
stantly referred to. The overlying Benton was very prolific in shells, as was the 
subjacent Carboniferous. In the Dakota, on the contrary, few forms were 
found, and these in restricted localities. In the general section, published in 
1870, only three species were mentioned from the Dakota, while the Benton is 
characterized by fifteen and the Pierre by more than twenty forms. The marine 
invertebrates referred to above, which were found in Saline county by Professor 
Mudge, were obtained from the lower part of the group, not many feet above the 
Permian. The shells were identified by Professor Meek. Other specimens were 
occasionally found in scattered localities, and were identified from time to time 
by Dr. C. A. White and others. The last of these descriptions by Doctor White 
appeared in 1894, and dealt with some shells from near Fairbury, Neb., found a 
little above the middle of the group.” 
Meanwhile the investigations of Hill in Texas and Cragin in southern Kan- 
sas had demonstrated the presence of vast beds of Lower Cretaceous rocks in 
these regions.*® In response to the invitation of Prof. A. W. Jones, of Salina, 
Kan., who had rediscovered the locality first found by Mudge in 1869, Professor 
Cragin visited Saline county, and in 1895 published a paper, in which he inclines 
to the opinion that the beds in central Kansas that are found at the base of the 
Cretaceous represent a northern extension of the Comanche or Lower Cretaceous 
of the Texas-Oklahoma regions.*| The position taken by Professor Cragin now 
has the assent of practically all geologists who have studied the question. 
In 1891 Dr. C. A. White published his ‘‘ Correlation Papers on the Cretaceous,’’ 
probably the most authoritative utterance so far written on the subject.” The 
Dakota horizon is regarded as a fresh-water deposit, constituting the basal mem- 
ber of the Upper Cretaceous. At that time, however, the deposit of its strata 
was not known to have immediately succeeded that of the Lower Cretaceous. 
These conditions have since been observed in several localities, notably in south- 
ern and central Kansas. Doctor White states that the Dakota is so well defined 
that no difference of opinion as to its identity, characterization and delimitation 
has ever arisen among geologists who have studied it in the southern interior re- 
gion, 7. €., south of the Platte river. The opinion is also expressed that we must 
rely almost exclusively upon fossil plants for the paleontological characterization 
of the horizon. 
During the last decade much work of permanent value has been done in the 
Dakota. Several publications of more than passing interest have appeared, but 
these must of necessity be passed byin thisreview. It may not, however, be inad- 
vised to mention the names of Lester F. Ward, Erwin H. Barbour, T. W. Stan- 
ton, N. H. Darton, Robert Hay, Charles S. Prosser, J. W. Beede, S. W. Williston, 
G. K. Gilbert, Geo. I. Adams, C. A. Fisher, W. N. Logan, F. W. Cragin, and A. 
W. Jones, all of whom have, either directly or indirectly, added to our knowledge 
of the Dakota Cretaceous of Kansas and Nebraska. 
GEOGRAPHICAL DISTRIBUTION. 
INTRODUCTION, 
It is not the province of this article to discuss the Dakota group beyond’ the 
limits of the states of Kansas and Nebraska, except the small area near Sioux 
City, in northwestern Iowa, and this only because of its early connection with 
39. Proc. U. S. Nat. Mus., 17: 131-138, 
40. Am. Jour. Sci., 50: 205-234. Also, Am. Geol., 16: 357-385. 
41, Am. Geol., 16: 162-165. 42, U.S. Geol. Sury., Bull. No. 82, 
