DESCRIPTIVE details: RIO PUERCO FIELD 625 



given. The fossils seen indicate a position near the base of the Mancos 

 about the horizon of the Tres Hermanos sandstone, and yet they occur 

 above a body of shale much thicker than any reported elsewhere below 

 this sandstone. 



Section of Part of Cretaceous Rocks 2 Miles Northeast of Lagttna, New Mexico 



Measured by N. H. Darton 



Feet 



Lava 



Sandstone 25 



Shale 60 



Sandstone, buff, massive, moderately soft 40 



Shale with sandstone layers, very fossiliferous ; contains Exogyra colum- 

 'bella Meek; Gh'yphoBa sp. ; probably a variety of G. newherryi; Avicula 

 gastrodes Meek?; Cardiiim sp. ; Panopea sp. ; Turritella sp. ; Rostel- 



lites volutoderma sp., and Fusus sp 



Sandstone, massive, hard, light buff 40 



Shale, dark gray to gray-green, sandy layers fossiliferous ; contains 

 Exogyra colurribella Meek; Pecten sp. ; Pinna petrina White; Inoce- 

 ramus 1 sp. ; Leda sp. ; Carditim sp. ; Lucina ? sp. ; Isocardia n. sp. ; 

 Cyprimeria? sp. ; Cortula sp. ; Liopistha (Psilomya) concentrica Stan- 

 ton ; Turritella ivhitei Stanton ; Tritonium Kanahense Stanton ; Actceon 



sp. ; Cintilia sp. ; Turrilites? sp., or Heteroceras sp 60 



Sandstone, hard, red, irony 5 



Sandstone, white, massive, part coarse 80 



Shale, greenish gray, sandy above 235 



Sandstone, hard, buff, massive 40 



Shale, soft 30 



Sandstone (basal bed of Cretaceous) 



Total 490 



No place was found where a complete detailed section of the Mesaverde 

 formation of the Eio Puerco field could be measured. The beds are well 

 exposed in only a few places, and where they are exposed some of them 

 are warped to such an extent that it is difficult to trace individual beds 

 for any considerable distance, and others are faulted so that certain beds 

 are duplicated; also, some of the upper part of the formation seems to 

 have been removed by erosion previous to the deposition of the overlying 

 Tertiary rocks, inasmuch as the lowest bed observed in the Tertiary is a 

 conglomerate. A generalized section was measured east of the Eio 

 Puerco, about 3 miles north of San Ygnacio, where many fossils were 

 collected. A section of the upper part of the coal-bearing rocks was 

 measured in detail about a mile farther north by L. C. Chapman, who 

 was assisting the writer in doing the field work. This has been incor- 

 porated in the general section below. Where the section was measured, 



