How was such symmetry of design created? Species by the score of tiny plants called algae and diatoms thrive in hot water, temperatures ranging from approximately 100° to 170° F. These plants have the capacity to assimilate silica held in solution, and as their lives are short they build sinter formations in the same manner as coral reefs are fashioned. These algae are, therefore, active geological agents in soil building on a considerable scale.[139] However, the intricate mineral incrustations and lacy embroidery surrounding the boiling hot springs and geysers are entirely the product of deposition due to evaporation. As the party progressed through the hierarchy of basins, Upper, Biscuit, Midway, and Lower, samples were taken and names given to many thermal features. They were leaving the Firehole region, but before an exit was made, or its spell broken, their whole experience was given a proper evaluation, and the greatest natural history idea of a millennium was born. On the evening of September 19, the explorers were encamped at the junction of the Firehole and Gibbon rivers. The setting was an impressive one. A majestic mountain backdrop cast long shadows upon them. The silvery Madison glided away in the foreground. On center stage, red embers of a neglected fire sparked and glowed in contact with a fanning breeze. The last scene was being enacted—the curtain was about to fall. It was an hour of recapitulation. Thrills were relived, confidences exchanged, speculations indulged. Then came the inevitable question of Yellowstone’s destiny. The question was posed, “Men and brethren, what shall we do?” “Why,” said Smith, “we’ll fence it in; give me Old Faithful.” “I’ll take the Falls,” echoed another. Serious consideration was given the idea of allowing each explorer to pre-empt a choice section in the most strategic location and pool the income for equal distribution. Whereupon, the inspired mind of Cornelius Hedges proposed and explained an idea that marked him as one of the far-sighted men of his generation. Said he: There ought to be no private ownership of any portion of this region. Rather the whole of it should be set apart as a great National Park for all time as a reserve for the use and enjoyment of all the people. Furthermore, each and everyone of us should make every effort to have this purpose accomplished.[140] The response was instantaneous and all but unanimous. The next day Langford wrote in his diary, “I lay awake half of last night thinking about it;—and if my wakefulness deprived my bed-fellow [Hedges] of any sleep, he has only himself and his disturbing National Park proposition to answer for it.”[141]