76 



ANNALS NEW YORK ACADEMY OF SCIENCES 



Fig. 30. — Section of the 

 Morrison formation 

 near Mack, Colorado. 



The overlying forma- 

 tion is the "Dakota," 

 and the underl.ving is 

 the La Plata sandstone. 

 Scale. 125 feet to 1 inch. 

 (Section b.v the writer.) 



19. Red sandstone or shale 



15. c. Clay, white at top 



h. Red shale 



a. Clay 



17. White, coarse, cross-bedded sandstone with 

 clay and shale members near the top .... 



16. c. Clay 



h. Sandy, compact clay 



a. Clay 



15. White, cross-bedded sandstone 



14. Clay 



13. Heavy, cross-bedded sandstone 



12. Clay, may cover sandstone or nodule layers. 



11. Sandstone 



10. Covered 



9. Heavy, cross-bedded sandstone. 



5. Variegated clay with lumps, especially at 



top 



7. Limestone 



6. c. Clays 



I). Sandstone 



a. Cross-bedded sandstone 



.5. Sandstones and clays alternating. Mostly 

 sandstones in beds 1-2 feet thick. Sand- 

 stone sometimes dies out and is replaced 

 by clay, with or without nodules 



4. Red sand clay with nodules 



3. Gray shale 



2. White sandstone with some clay 



1. Pinkish white sandstone 



Feet 



7 



1 



25 



30 



16 



1 



271/2 

 17 

 30 

 23 

 57 

 1 

 22 

 31 



16 

 2 



52 

 15 



25 e. 



20 



25 



7 



24 



80 



Total 766 



The Morrison is underlain by the La Plata 

 sandstone in most of the southwestern Colorado 

 areas, with apparent conformity. Beneath the La 

 Plata, which is Jurassic in age, there is a well 

 marked stratigraphic break. At different locali- 

 ties the La Plata lies upon the Dolores beds, of 

 Triassic age, upon the Cutler and Hermosa for- 

 mations, of late Paleozoic age, and upon pre-Cam- 

 briaii crystallines (Cross and Larsen, 1914, 7). 



The McElmo formation near Green Eiver, Utah, 

 has been recently described by Lupton (1914, 3). 

 It is from 1000 to 1200 feet thick at this place. 

 Marine fossils in the lower part indicate, however, 

 that part of the beds included in Lupton's section 

 may belong to the underlying Jurassic beds. 



The section is as follows : 



