268 Annals of the Carnegie Museum. 



second division is being studied by the members of the State Geo- 

 logical Survey of North Dakota, and the results published in the 

 biennial reports of that organization. This state is also fortunate in 

 having its geological history recorded in a scientific book of unusual 

 interest and clearness, "The Story of the Prairies," by Daniel E. 

 Willard. The present writer, however, is able to add something to 

 the knowledge of the geology of North Dakota. 



Montana has no state geological survey, and aside from the quad- 

 rangles mapped by the United States Geological survey, the work, 

 like that recorded in the present paper, has been of an itinerary na- 

 ture. Perhaps no one who has not studied the regions through which 

 Dr. F. V. Hayden led his geological expeditions over thirty years 

 ago, can fully appreciate the work of that careful observer and far- 

 seeing geologist. It is not strange that he made so many mistakes, 

 but it is a wonder that he was so nearly right ; nevertheless every year 

 discoveries in the west modify our ideas of the past history of our 

 continent, and enable us to approach the truth a little more nearly. 



By far the best section of the Cretaceous and Lower Tertiary with 

 which I am acquainted is that in the region of Fish and Mud Creeks 

 northeast of Melville in T. 5 & 6 N., R 16 & 17 E., in the northern 

 part of Sweetgrass County in Montana (Plate XX). Here series of 

 strata which are separable into fifteen or more distinct divisions and 

 range from doubtful Jurassic to Lower Eocene, occur in a beautiful suc- 

 cession of rocks several thousands of feet in thickness ; and the condi- 

 tions are such that nearly every minor division can be studied in detail 

 in some portion of the area. Fossils have been found at about twenty 

 different levels and more careful search will undoubtedly reveal many 

 more. It is extremely desirable that a thoroughly detailed study of this 

 section be made, as this could not fail to aid greatly in the solution of 

 some interesting problems in the Mesozoic and Cenozoic geology of the 

 west. This section has the additional advantage of being located in 

 an intermediate position between the great plain and the Cordilleran 

 region, the physical conditions of which at the present time are so 

 dissimilar and the geological histories of which have been so very 

 different. 



A generalized section of this region, which will give some idea of 

 the different horizons, is given here. This will furnish a convenient 

 scale for reference in dealing with the geology of other localities. A 

 description, intentionally brief, of the principal horizons, was given 



