S40 



N.l TV RE 



[Oct. 25, 1877 



to Cheyenne in Wyoming, and ihence westward by ihe 

 Central Pacific Railway.'across the range to Ogden, and 

 the Great Salt Lake in Utah, which lies on the base of 

 the Wahsatch Mountains, themselves the western escirp- 

 ment of the Rocky Mountains proper in that latitude. 

 After ascending these we proceeded westward by rail 

 through Utah, to Nevada, thus crossing the great dry 

 region that intervenes between the Rocky Mountains and 

 the Sierra Nevada, which is variously known as the Desert, 

 Salt, or Sink region of North America, in accordance 

 with the prevailing features of its several parts. It is 

 elevated 3,000 to 4,000 feet, and traversed by numerous 

 short meridional mountain-ridges, often reaching 8,000 

 feet, and rarely 10,000 feet elevation ; unlike the Rocky 

 Mountains or over the Sierra Nevada, these present no 

 forest-clad slopes, or even a sub-Alpine flora. 



From Reno, at the western base of the Sierra Nevada, 

 we proceeded south by Carson City, flanking the Sierra 

 for some sixty miles to Silver Mountain, when we stiuck 

 westwards, ascending the Sierra, which was crossed 

 obliquely into the Pacific slope. There we visited three 

 groves of the ' Big Trees ' {Sequoia gigantca) at the 

 headwaters of Stanislaus and Tuolome Rivers, and 

 the singular Yosemite Valley, whence we descended 

 into the great valley of California, and made for San 

 Francisco. 



From the latter place we made excursions first to the 

 old Spanish settlement of Monterey, which is classical 

 ground for the botanist, as being the scene of Menzies' 

 labours during the voyage of our countryman, Capt. Van- 

 couver, in 1798 (whose surveys are held in the highest 

 estimation by Prof. Davidson and the officers of the Coast 

 Survey of the United States), whom he accompanied as 

 botanist. Then we went northwards along the coast 

 range to Russian River to visit the forests of Red-wood 

 {Sequoia seiupervitots), the only living congener of the Big 

 Trees, and almost their rival in bulk and stature. Then 

 to Sacramento, and up the valley of that name for 150 

 miles to Mount Shasta, a noble forest-clad volcanic cone 

 about 14,400 feet in elevation. Returning thence to 

 Sacramento we took the Union Pacific Railway east- 

 wards, and from the highest station visited Mount Stan- 

 ford, on the crest of the Sierra Nevada, and Lake Taho, 

 which occupies a basin in the mountains at about 7,000 

 feet elevation, and with which _we finished our western 

 journeyings. 



In California the Coniferx were a principal study, 

 with a view of unravelling their tangled synonymy and 

 tracing the variations and distribution of these ill-under- 

 stood trees, which attain their maximum development in 

 number of species and in statureon the Pacific slope of 

 the American continent. 



The net result of our joint investigation and of Dr. 

 Gray's previous intimate knowledge of the elements of 

 the American flora is, that the vegetation of the middle 

 latitudes of the continent resolves itself into three prin- 

 cipal meridional floras, incomparably more diverse than 

 those presented by any similar meridians in the old 

 world, being, in fact, as far as the trees, shrubs, and 

 many genera of herbaceous plants are concerned, abso- 

 lutely distinct. These are the two humid and the dry 

 ntermediate regions above indicated. 



Each of these, again, is subdivisible into three, as 

 follows : — 



1. The Atlantic slope plus Mississippi region, sub- 

 divisible into («) an Atlantic, (/i) a Mississippi valley, and 

 (y) an interposed mountain region with a temperate and 

 sub-alpine flora. 



2. The Pacific slope, subdivisible into (a) a very 

 humid cool forest-clad coast range ; O) the great hot, 

 drier Californian valley formed by the San Juan river flow- 

 ing to the north, and the Sacramento river flowing to the 

 south, both into the Bay of San Francisco ; and (y) the 

 Sierra Nevada flora, temperate, sub-alpine, and alpine. 



3. The Rocky Mountain region (in its widest sense 

 extending from the Mississippi beyond its forest region to 

 the Sierra Nevada), subdivisible into (o) a prairie flora ; 

 (/3) a desert or saline flora ; (y) a Rocky Mountain proper 

 flora, temperate, sub-alpine, and alpine. 



As above stated, the difference between the floras of 

 the first and second of these regions, is specificall »-, and 

 to a great extent generically absolute ; not a pine or 

 oak, maple, elm, plane, or birch of Eastern America 

 extends to Western, and genera of thirty to fifty species 

 are confined to each. The Rocky Mountain region 

 again, though abundantly distinct from both, has a few 

 elements of the eastern region and still more of the 

 western. 



Many interesting facts connected with the origin and 

 distribution of American plants and the introduction of 

 various types into the three regions, presented them- 

 selves to our observation or our minds during our 

 wanderings ; many of these are suggestive of comparative 

 study with the admirable results of Heer's and Les- 

 quereux's investigations into the pliocene and miocene 

 plants of the north temperate and frigid zones, and which 

 had already engaged Dr. Gray's attention, as may be 

 found in his various publications. No less interesting 

 are the traces of the influence of a glacial and a warmer 

 period in directing the course of migration of Arctic 

 forms southward, and Mexican forms northward in the 

 continent, and of the effects of the great body of water 

 that occupied the whole saline region during (as it would 

 appear) a glacial period. 



Lastly, curious information was obtained respecting the 

 ages of not only the big trees of California, but of equally 

 aged pines and junipers, which are proofs of that 

 duration of existing conditions of climate for which 

 evidence has hitherto been sought rather amongst fossil 

 than amongst living organisms. 



I need hardly add that the part I played in the above 

 sketched journey was wholly subordinate to Dr. Gray's, 

 who had previously visited both the Rocky Mountains 

 and California, though not with the same object. But 

 for his unflinching determination that nothing should 

 escape my notice which his knowledge and observant 

 powers could supply, and Dr. Hayden's active co-operation, 

 my own labours would have been of little avail. 



Moreover, throughout the expedition we experienced 

 great hospitality, and enjoyed unusual facihties, not only 

 from the staff of the Geological Survey, but from the 

 railway authorities, who franked us across the continent, 

 and on all the branch lines which we traversed. 



J. D. Hooker 



