THE BASIN PROVINCE 155 



"The sandstones are mainly quartzose, the grits contain much feldspar, mica, 



and small pebbles like the larger ones of the conglomerates. The latter contain 



pebbles of granite, gneiss, and various schists, of quartzite and limestone, of 



greenstone and porphyry, and many of red, pink, smoky, or white quartz, part 



•of which may come from veins. 



"The pebbles are in general larger near the San Juan mountains. Boulders 

 a foot in diameter are occasionally present, but most pebbles are only a few inches 

 in diameter. The relative abundance of different rocks among the pebbles varies 

 according to locality. * * * 



"Taking the formation as a whole, the grits and conglomerates comprise about 

 one-third or less of its total thickness in the quadrangle surveyed, and they are dis- 

 tributed throughout the section. It may be assumed that as distance from the 

 source of the pebbles increases, the formation becomes more and more a series of 

 fine-grained sandstones and shales, with subordinate grits and conglomerates. 



" Typical section composed of two sections made in the Dolores valley a few miles below Rico. 



Top. Feet. 



60. Coarse sandstone or grit, cross-bedded, locally conglomeratic, rather purplish in tone 100 



59. Calcareous sandstones, sandy shales, often micaceous and fissile, either red or mottled red and 



green in color 120 



58. Grit-conglomerate, of variable texture, forming ledge outcrops 10 



57. Fine-grained calcareous sandstones, sandy shales, with occasional thin layers of harder sandstones 



in red or variegated red and green 80 



56. Sandy shales, with thin sandstones at intervals; variegated or mottled dark red and light green; 



have peculiar nodules 55 



55. Grit-conglomerate 20 



54. Calcareous sandstone or sandy shale 100 



53. Grit-conglomerate, very similar to number 60 30 



52. Friable sandstone 35 



51. Grit-conglomerate, hard and forming a prominent ledge outcrop 15 



50. Sandy shales and crumbling sandstone, strong red color, partly calcareous no 



49. Calcareous shales 20 



48. Coarse arkose sandstone 30 



47. Calcareous shales 30 



46. Sandstone variegated 20 



45. Calcareous shales 15 



44. Coarse sandstone, friable, variegated 15 



43. Hard standstone, with few small pebbles of quartzite 15 



42. Dark-red sandy shales; in places calcareous and then massive; in other parts micaceous and then 



fissile 90 



41. Compact arkose sandstone, with few pebbles; cross-bedded; friable sandstones near top 15 



40. Calcareous clay, or marl, reddish, with spots of various shades 33 



39. Friable sandstone, largely quartzitic, variegated in color 15 



38. Conglomerate and arkose grit; most conglomeratic in center; a grit with some pebbles in upper 



and lower portions; pebbles of greenish slates and schists, quartzite, granite, and greenish 



porphyry 30 



37. Calcareous shales, fine-grained, variegated 30 



36. Fine-grained, reddish shale 15 



35. Massive sandstone, coarse-grained, cross-bedded, streaked with light-colored layers; some shaly 



partings 15 



34. Friable sandstone, purplish and grayish layers alternating irregularly 20 



33. Sandstones, finely laminated, compact, cross-bedded, variegated 25 



32. Calcareous clay shales, graduating into more massive sandy shales and a rather tough sandstone. 10 



31. Sandstone, micaceous, red or green, carrying a thin layer of coarse conglomerate near the top. ... 10 



30. Arkose sandstone, cross-bedded, white 20 



29. Sandstone, micaceous, red and green 6 



28. Arkose sandstone, coarse grained, white 7 



27. Sandstone, compact, micaceous, salmon color to red 10 



26. Calcareous shales, green and brown 5 



25. Sandstone, micaceous and compact, containing layers of gnarly limestone from 2 to 12 inches 



thick 18 



24. Calcareous sandstone, generally red, but mottled; contains thin layers of gnarly limestone 15 



