CRETACEOUS FORMATIONS 327 



gesta Conrad ?, Camptonectes sp. Scaphites veatricosus Meek and Hayden, 

 Anomia sp., Tellina sp. Among these the Iaoceramus, Prionotropis, and 

 Scaphites are classed as characteristic Benton forms. 



The topographic relations of the Dakota outcrop on Kennedy creek 

 and the highest Benton outcrops under Chief mountain are such that if 

 the beds were strictly horizontal the thickness of Cretaceous rocks would 

 be 2,700 feet. As there is a slight dip from the former beneath the latter, 

 this may be increased to 3,500 feet or more. It is, however, possible that 

 the overthrusts which traverse the Algonkian are paralleled by others in 

 the apparently undisturbed Cretaceous beds, and, if so, no estimate of 

 thickness can be based on the meager data now available. 



Just northeast of the northern end of Lower Saint Mary lake Weller 

 collected from a gray sandstone and according to Stanton's determina- 

 tion obtained Inoceramus sp., possibly young of /. labiatus, Mactra em- 

 monsiMeek? Tellina mo desta Meek, Donax cuneata Stanton, Corbula sp., 

 Turritella sp., and Lunatia sp. Of these Stanton says : 



"Although the evidence of .these fossils is not absolutely conclusive as to the ho- 

 rizon, it is probable that they are from the Benton or at least from some horizon 

 within the Colorado group." 



Laramie, — Ten miles east of Lower Saint Mary lake, on the Middle 

 fork of Milk river, occur outcrops of thin-bedded and cross-bedded gray- 

 sandstone and arenaceous shale. Some of the layers contain scattered 

 and fragmentary plant remains. Others are barren of fossils. Certain 

 ones are composed of oyster shells. In a section measuring 70 feet 

 Weller found five oyster beds, from which he collected Ostrea glabra 

 Meek and Hayden, Corbicula occidentalis Meek and Hayden, and small 

 specimens of an undetermined Melania, which may be the young of If. 

 wyomingensis Meek. The Ostrea of the highest stratum is said by Stanton 

 to approach more nearly to O. subtrigonalis Evans and Shumard. These 

 are all classed as belonging to the Laramie fauna. 



TERTIARY LAKE BEDS OF NORTH FORK 



On the North fork of the Flathead there are, as already stated, bluffs 

 of clay with interbedded sandstones and lignites, in which no fossils 

 were found. Details of constitution are summarized in the tabular state- 

 ment of formations. The materials, degree of induration, and the lig- 

 nitic condition of the carbonaceous deposits serve to indicate that they 

 may be of Miocene # or Pliocene age, as are beds near Missoula, which 

 they resemble. These deposits are called lake beds because they are 

 very distinctly and evenly stratified. They consist of fine sediment, 

 such as would settle from quiet water only, and they occur in a valley of 



