RELATION OF PLANT PROTOPLASM TO ENVIRONMENT. 257 



steadily diminishing amount compared with the areas occupied during more and 

 more remote ages of the past. Weed says regarding the Yellowstone region: 

 "There is perhaps no other district in the world where hydrothermal action is as 

 prominent or as extensive as it is in the Yellowstone Park. In this area of about 

 3,500 square miles, over 3,600 hot springs and 100 geysers have been visited 

 and their features noted, and there are also almost innumerable steam vents." 

 But there are many geological evidences to prove that back to the time of the 

 Cambrian and the Archaean or Proterozoic epochs such areas were evidently 

 greatly more extended than now. There is no reason therefore to suppose that 

 such simple algae, carrying on the active rock-forming function that they do, were 

 absent from the waters of such areas as the above, where an abundant food supply 

 existed for them, that might be scant and hard to obtain elsewhere, either in 

 cooler waters, on land, or in the sea. So we may well accept it as highly probable 

 that some of these thermophilic algae correspond, so to speak, to the Tcrebratulas 

 and the Lingulas of the animal kingdom, in that they are very probably forms 

 which have lived on through the ages, and through uniform environmental con- 

 ditions, that represented their primitive environmental surroundings. 



With increasing cooling of the earth's mass, derived species may have 

 branched off from them that became modified to less stimulating or to chemically 

 more restricted surroundings, and which would account for the numerous species 

 of Schizophyceae now living, some in fresh water, some on land, some in saline 

 or in brackish regions, some by the seashore. If we bear in mind also the strongly 

 mineral nature of the geyser waters, we need not wonder that such areas as 

 Salt Lake show extensive beds of blue-green algae like Microcystis packardii; 

 that Oscillatoria salinarum can flourish in the escaped liquor from the salt works 

 of Porto Rico, or that Ccelosphceriopsis halophila should live in a salt lagoon of 

 the Hawaiian Islands. Synechococcus curtus again is said by its discoverer Gardner 

 to have been found "floating in myriads in hot salt water, near Key Route 

 power house, Oakland" (4). 



Instead therefore of regarding the thermophilic algae as acclimated species, 

 there is equally good or even more abundant reason for considering, that they 

 now inhabit surroundings which have remained little if at all altered from the 

 period of their early evolution. 



Fifth. Under this caption it might be observed that freshwater limestones, 

 lime silicates and siliceous rocks, which often show few or no traces of organic 

 remains, occur in most of the geological formations back to the Archaean epoch. 

 At times they occur in a pure, at times in a more or less impure state. The 

 thickness of the beds varies greatly from a few inches to many feet. Opinion 

 was long divided as to their origin, but their probable vegetable formation is 

 being more clearly emphasized. Thus speaking of the later Archaean or Proter- 

 ozoic rocks Geikie (8) says: " these ancient stratified formations do not consist 

 merely of clastic sediments. They include important masses of limestone and 

 dolomite, sometimes highly crystalline, but elsewhere assuming much of the 



17 JOURN. ACAD. NAT. SCI. PHILA.. VOL. XV. 



