proceedings: geological society 9 



The distribution of the Dakota sandstone about the present moun- 

 tains and its attitude toward them; its presence within the mountains at 

 great altitudes; and its relation to the older formations seem to prove 

 that the Dakota sandstone extended practically continuously over the 

 present mountain region. 



The distribution of the marine sediments of Colorado age, that lie on 

 the Dakota sandstone, is essentially the same as that of the Dakota, 

 that is, they occur on both sides of the mountains and at numerous 

 places within the mountain region and their lithologic character is not 

 such as to indicate that they were derived from the present mountain 

 area rather than from the continental land masses that existed both east 

 and west of the interior Cretaceous sea. Their presence near Brecken- 

 ridge, Colorado at an altitude of 13,4000 feet, and in many other places 

 at nearly as great altitudes, proves that these places at least were below 

 sea-level in Colorado time, and an inspection of their distribution leaves 

 little room for doubt that they were deposited continuously over the 

 mountain region. 



The sedimentary rocks of Montana age in the Rock\' ^Mountain region 

 are more variable than those of Colorado age, but their general lithologic 

 character does not seem to harmonize with the postulate that any con- 

 siderable part of them was derived from the present .mountain area. 

 In general, the marine shale formations thicken toward the present 

 mountains while the sandstone formations thicken away from tha moun- 

 tains. In brief, the Upper Cretaceous formations behave as if no Rocky 

 ]\Iountains existed when they were laid down. 



If the Rocky Mountain region was covered with Cretaceous sedi- 

 ments, it follows that this region must have been uplifted and the 

 older rocks exposed to erosion before the conglomerate, consisting of 

 pebbles of these older rocks, could have been formed. 



The 274th meeting of the Society was held in the Cosmos Club on 

 November 12, 1913. 



Under informal communications ISlr. Edson S. Bastin discussed the 

 origin of the titaniferous iron ore at Caribou, Colorado. These ores 

 occur within small, irregular bodies of gabbro which in turn lie within 

 a large stock of monzonite. There is clear field evidence that both 

 gabbro and iron ores are magmatic differentiations from the monzonite 

 magma. The differentiation has proceeded along two lines leading to 

 the formation wdthin the same gabbro mass of (1) iron ores composed 

 essentially of augite, magnetite and spinel, and (2) ores much richer in 

 magnesia composed of olivine and magnetite. The chemical changes 

 during differentiation were shown by plotting a number of analyses of 

 these rocks and ores in diagrammatic form. 



REGULAR PROGRAM 



The change of optical and crystallographic properties of quartz with tem- 

 perature. F. E. Wright. This paper is published in full in Jour. Wash. 

 Acad. Sciences, 3, 485. 1913. 



