30 W. Cross — Post- Laramie Deposits of Colorado. 



nient aside from the general stratigraphical position. Mr. 

 Cannon, however, collected a number of fossil shells from the 

 shales below the breccia about one mile east of Hot Sulphur 

 Springs, and on the south side of Grand river, that is, on the 

 western flank of the " breccia spoon." These shells were sub- 

 mitted to Dr. C. A. White for determination. The following 

 species were found at 15 feet below the " breccia : " Pteria 

 parke?isis White, Scaphites nodosus Owen, sp., Ostrea trans- 

 lucida M. & H., Leda {Yoldia) scitula M. & EL, Inoceramus 

 convexus M. & H., I sagvnsis Owen, Baculites ovatus Say, B. 

 compressus Say?, Placenticer as placenta, De Kay, sp., and 

 Dr. White is of the opinion that they indicate the lower or 

 Ft. Pierre division of the Montana rather than the Fox Hills. 



Marviue's description of the mechanical constitution of the 

 " lignitic " series is generally applicable to the part above the 

 " doleritic breccia," but as regards the character of the mate- 

 rials composing both parts of the series some important cor- 

 rections are to be made. In the first place the " doleritic 

 breccia" was unfortunately named, for the rocks composing 

 the complex are andesites as far as examined, and the entire 

 mass seems to be a water-arranged deposit containing finely 

 preserved leaves in some of the most massive parts. The beds 

 are very irregular in thickness, and are decidedly thicker on 

 the eastern border of the area than on the western. 



As to the great series succeeding the dark massive beds, Mar- 

 vine was in error in stating that they consist entirely of 

 Archaean debris, for they contain andesitic material in very 

 variable amount for more than 2000 feet above the dark brec- 

 cia, and the whole series is evidently one. The character of 

 the eruptive material changes somewhat upward in the series, 

 lighter colored and more acid rocks prevailing. Many beds in 

 the terraces north of Grand river are sandstones or grits con- 

 sisting of quartz and feldspar to a strongly prominent degree 

 but none are entirely free from andesitic fragments, and con- 

 glomerates composed very largely of eruptive material often 

 succeed quartzose sandstones. The strata in the divide be- 

 tween Middle and North Parks belong to the same series, 

 according to Marvine. These were not visited by the writer, 

 but the beds shown in the high ridges some eight miles north 

 of Grand river, east of Whiteface Mountain, still carry a large 

 amount of pinkish andesitic material. The same eruptive 

 constituents were found in the strata of Mt. Bross, and of the 

 ridges south of Hot Sulphur Springs ; in fact, no beds of this 

 complex were found to be wholly free from materials of this 

 character. 



No animal remains are reported from the series by Marvine, 

 nor were any found by either Mr. Cannon or the present 



