ATION OF PALEOZOIC FORMATIONS. 211 



of the sedimentaries, especialh^ of the Red Beds, upon the Archean, and their failure 

 to cross the summits of the ranges, and was developed from the theory that the existing 

 Paleozoic series (for it is only to Paleozoic time that these remarks refer) represents 

 more or less uninterrupted sedimentation. Similarly, in discussions of the subject, 

 Paleozoic time has been for the most part lighth^ touched upon and treated in general 

 terms as if the conditions which prevailed were in the main uniform. Writing in 

 1893 of the Rocky Mountains of Colorado," Emmons recognized five great marine 

 transgressions, the post-Archean, the post-Algonkian, the late Paleozoic, the late 

 Jurassic, and the post-Cretaceous. The first disturbance recognized subsequent to 

 the Algonkian therefore is placed in the late Paleozoic, and probably this conclusion 

 is connected with the occurrence in the conglomerates of the Maroon formation in 

 the Elk Mountains of pebbles containing Carboniferous fossils. Again, in the Ten- 

 mile folio, published in 1898,* he remarks that deposition was more or less contin- 

 uous from the Upper Cambrian to the Trias, without evidence of any change in the 

 relations of the sea bottom to the successive sediments, and that the first orogenic 

 disturbance probably occurred in the Jurassic. 



Much evidence has now accumulated, however, tending to show that the Paleozoic 

 series is anything but continuous and complete. This is indicated by the frequency 

 of unconformities, sometimes by erosion, sometimes by overlap, by the thinness of 

 the remaining beds, and by their unequal distribution. That some of the intervals 

 were of protracted duration is shown by the extent of the time break between 

 apparently consecutive formations. The often much greater gaps indicated where 

 different Paleozoic formations rest directly upon the granite is probably not so much 

 the product of a single erosion period or a single transgression as the sum of a 

 number of briefer ones and the resultant of a complicated series of movements. The 

 permanence of these Archean islands seems to me to involve an a priori improbability, 

 from the fact that they must have been reduced almost to sea level long before the 

 immeasurable stretch of Paleozoic time had ela^jsed, so that even slight oscillations, 

 which during so long a period could hardl}' have failed to occur, would have sufiiced 

 to submerge them. 



That the Paleozoic series in Colorado is reallj' an extremely disconnected one 

 is shown by the number and extent of the gaps that are known to occur in it, and 

 an intimation of this is to be found in the greatly reduced thickness of the pre- 

 Carboniferous series, considei'ed as a whole and in relation to areas farther east and 

 farther west. The Cambrian so far as it is known is represented by only a few hun- 

 dred feet, all of which belongs to the Upper Cambrian. All Lower and Middle Cam- 

 brian time appears to be unrepresented. The Ordovician must be approached with 



a Int. Geol. Cong., Comt. Rend., oth sess. (1891), 1893, p. 404. 

 bV. S. Geol. Surv., Geol. Atlas United States, folio 48, 1898. 



