142 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



ingston fields are much cross-bedded, while in Cleveland and Big 

 Sandy fields, rippled surfaces were observed and the shales aiid 

 sandstones are in rude lenses. So also in the Milk River field 

 where all deposits are lens-like and the sandstones are cross-bedded. 

 In Teton County, the Two-Medicine formation is characterized by 

 great irregularity of the deposits and fossil wood abounds ; the Vir- 

 gelle (Lower Eagle) sandstone is coarse and cross-bedded. The 

 conditions in Alberta are similar ; the Belly River sandstones have 

 been described as cross-bedded, rippled and marked by trails ; the 

 same features were observed farther north on Pine River. 



The Benton in New Mexico, has, near the base, the Tres Her- 

 manos sandstone, cross-bedded, rippled and locally conglomeratic, 

 w^iich persists to the northeastern corner of the San Juan Basin. 

 Similar features are recorded in the southwestern part of that basin 

 as well as from localities in the Uinta Basin. The Dakota is usually 

 more or less cross-bedded and holds local conglomerates. The 

 Kootenai of New Mexico is cross-bedded and locally conglomeratic; 

 it is rippled, cross-bedded, locally conglomeratic in the Black Hills, 

 where petrified wood, chiefly cycads, is abundant. The conditions 

 are similar in Montana, while in Alberta the same features were 

 dbserved at many localities. 



These features, characterizing the rocks of the several forma- 

 tions, indicate deposition in, at most, shallow water, as well as sub- 

 sequent exposure to subaerial conditions. The rippling and cross- 

 bedding were due to water movements in probably most cases, but 

 it is possible that there has been too great readiness to accept this 

 mode of origin as almost universally applicable. The writer has 

 observed the ripple marks in rocks of several formations and has 

 compared them with wind ripples seen by him in the sandy areas in 

 the western states and in Russia and Prussia, as well as on broad 

 river benches. The resemblance to fossil ripples, seen in many beds, 

 is so great that the mode of origin must be the same for both. It 

 may be also that some of the "cross-bedding" was due to wind 

 action. The complex structure shown in many diagrams is precisely 

 that of the seolian limestone of Bermuda and observable more or 

 less distinctly in many dunes ; the " current bedding " is clearly due 

 to stream action. The presence of tree stumps and logs is evidence 



