876 HISTORICAL GEOLOGY. 



The laccolitlis of the Henry Mountains in southern Utah (page 301), 

 according to Gilbert's descriptions, are other products of this time of dis- 

 turbance; and so also, as remarked by Hills, those of the Spanish Peaks in 

 southern Colorado. 



Other eruptions of the epoch contributed to the making of some of the 

 remarkable silver and lead mines of the Rocky jNIountain region. S. F. 

 Emmons, in his excellent Report on the famous Leadville region (page 340), 

 briefly considers the question of the age of the veins. He points out the 

 fact that some of the largest eruptions preceded the Laramie upturning, 

 while others attended the upturning ; but he leaves the question as to the 

 precise time of vein-making undecided. Emmons also considers it probable 

 that a large part of the eruptive rocks of Colorado are of the same Laramide 

 epoch. 



According to Iddings, the igneous eruptions in Wyoming and Montana and the 

 adjoining Yellowstone Park went on near, and at, tlie close of the Cretaceous. The rocks 

 are largely andesytes of various kinds, much like those of Colorado. Tliey occur as 

 dikes, intrusive sheets, and laccolitlis ; and later in the epoch of eruption, probably in the 

 early Tertiary, volcanic cones were thrown up. In Montana similar eruptive conditions, 

 of the same epoch, have been observed by J. E. Wolff (1892) in tlae Crazy Mountains, 

 producing intrusive sheets ; and among the rocks occur elseolite syenyte, and varieties 

 containing nephelite and sodalite. Similar rocks occur, according to Lindgren (1890, 

 1893), in the Higliwood Mountains, farther north. 



The occurrence of dikes of sandstone., as described by Cross (1894), in the granite of 

 the region of Pike's Peak, evidently filling fissures in the granite, may be mentioned here, 

 although their time of origin is uncertain. They occur on the west side of the Manitou 

 Park. They are narrower below, and sometimes branch downward. The width varies 

 from 300 yards to a few inches and even a thin film. The rock is an even-grained 

 quartzose sandstone, usually as hard as quartzyte, with some limonite among the grains 

 as cement. 



In India the eruption of the "Deccan traps," the most enormous on 

 record, took place probably, according to Blanford, at or near the close of 

 the Cretaceous. The facts are mentioned on page 299, under the subject of 

 non-volcanic igneous eruptions. The eruptions at the close of Mesozoic time 

 mark the commencement of an eruptive period in the earth's history, which 

 had its maximum effects during the following Tertiary period. 



Disappearance of species. — The disappearance of species at the close of 

 Mesozoic time was one of the two most noted in all geological history. 

 Probably not a tenth part of the animal species of the world disappeared at 

 the time, and far less of the vegetable life and terrestrial Invertebrates ; 

 yet the change was so comprehensive that no Cretaceous species of Vertebrate 

 is yet known to occur in the rocks of the American Tertiary, and not even 

 a marine Invertebrate. The only species in North America known to have 

 continued on into the Tertiary are plants, some of Avhich existed still in the 

 Miocene, and a few differ little from existing species. Here ended not only 

 the living species of Dinosaurs, of Mosasaurs, and Pterosaurs, but these 

 tribes of Reptiles. This was true also of the Belemnites, so far as 



