THE CRETACEOUS PERIOD. 361 



and fresh water. The Laramie appears to mark the transition from the largely 

 marine deposits of the Montana to the fresh-water and land conditions of the 

 Tertiary. 



It is evident that the Cretaceous was marked by many water areas in which 

 hydroseres could develop. The abundance of brackish areas and of coal- 

 forming marshes indicates that the hydroseres were largely haloseres and oxy- 

 seres during the Colorado and Montana epochs. Bare rock areas probably 

 occurred throughout the period in the Rocky Mountains, but they were 

 apparently most abvmdant during the gradual sea withdrawal of the later 

 Montana and the Laramie. The climate appears to have been warm, moist, 

 and fairly equable throughout, though it seems probable that much cooler or 

 drier areas occurred at the highest elevations and in the region of the Great 

 Basin. 



Life-forms and dominants. — ^Apparently all of the life-forms known for the 

 region to-day were present during the Cretaceous. Among the blue-green 

 algse Gloeoconis and Zonotrichites are recorded, while the presence of bacteria 

 in the Jurassic implies a considerable evolution of their blue-green ancestry. 

 Diatoms had appeared in the Liassic, and Chlorophyceae in the Permian. 

 Nostoc is recorded for the Tertiary, but it is probable that it had appeared 

 long before. While Kchens are practically imrecorded before the Tertiary, the 

 fact that most of these are of the highest type, e. g., Parmelia, Ramalina, 

 Sphaerophorus, Cladonia, etc., indicates that fungi had assimied this habit 

 long before. This is supported by the fact that hchen-forming fungi had 

 already appeared ia the Carboniferous. Liverworts had developed, such as 

 Paleohepatica in the Jurassic, and Marchantites, Blyttia, and Jungermannites 

 in the Comanchean. Authentic mosses are of the rarest, but Musdtes and 

 Fontinalis seem to indicate their presence beyond much doubt. 



As a legacy from the Paleophytic and Mesophytic, ferns and fernworts were 

 abundant, though of subordinate and constantly decreasing importance. 

 Asplenium, Dicksonia, Dryopteris, Gleichenia, Onodea, Osmunda, Pteris, 

 Eguisetum, Lycopodiwn, Selaginella, etc., occurred throughout. Cycadales 

 were still more or less abundant, though the Bennettitales were apparently 

 rapidly disappearing, since none are recorded for the Tertiary. Gymnosperms 

 were abundant, and many genera such as Araucaria, Podocarpus, Sequoia, 

 Ginkgo, etc., were much more dominant and widely distributed than they 

 are to-day. 



In the characteristic angiospermous flora the "Tables of Life-Forms and 

 Dominants" show that each associes of the hydrosere was represented in the 

 Cretaceous. Chara, Lemna, and Potamogeton represented the submerged 

 form, Brasenia, Castalia, Nelumbo, Lemna, Potamogeton, and Trapa the float- 

 ing form, and Phragmites, Typha, Cyperadtes, and Carex the reed and sedge 

 forms. While grasses and herbs are almost unrecorded, except for aquatic 

 genera, the presence of Phragmites, Trapa, and other relatively high forms 

 shows that they must have been in existence. It is not improbable that ferns, 

 equisetxuns, and cycads still played the r61e of grasses and herbs in part, as 

 they did exclusively in the two preceding eras. The scrub of arid areas 

 perhaps stUl consisted partly of cycads in the broad sense, though angio- 

 spermous scrub had certainly developed to a considerable and probably a 

 predominant degree, as indicated by Andromeda, Betula, Ceanothus, Cornus 



