OCT., 1899.] SLOPE EXPOSURE. 49 



Canyon, .lear the mouth of Clear Creek (see pi. iii). Tiie altitude of 

 the bottom of the canyon at this point is 0,700 feet, which would nat- 

 urally i)lace it in the middle of the Canadian zone. The steep west 

 side of the narrow ridge between the two creeks receives the afternoon 

 sun at nearly a right angle, and is in consequence an unusually warm 

 slope for the altitude. The result is that seeds of plants carried upward 

 by winds and birds from the Transition zone, more than 1,000 feet 

 below, have here found a favorable resting place and have grown into 

 a colony of Transition zone species, among which are Abies eoncolor 

 loiciana, Arvtostaphi/los patula, Kmizia trUhntata., Amelanchier abiifolia, 

 Biibus parvifiorus, Sorhus fiambuci folia, Symplioricarpos pilosus, Bibes 

 viscosissimKm, B. amiction, iS((nibuc7(s melanocarpa, Apocynum. pumihim^ 

 ISpira'a doiKjIasi, Vaccinimn {arbuscula*), Liipinus elmeri, Eriogonum 

 marifolium, Gilia aggregata, Pteris aquilina lam(gi7iosa, and the large 

 Transition zone form of CasiiUeja miniatu. Just across the canyon, 

 and in one place less than 100 feet from the lower edge of this isolated 

 Transition colony and at a lower level, are species belonging to the 

 Hudsonian zone — such as Pentstemon neivberryi and Pulsatilla oeviden- 

 talis. Thus, growing close together on opposite slopes of the same 

 canyon, are species characteristic of zones both above and below the 

 one to which the altitude properly belongs. This case is by no means 

 peculiar and is a good illustration of the simpler effects of slope exposure 

 commonly shown in mountain canyons. 



Another class of cases is found on the buttes and hills. A mile 

 and a half northeast of Wagon Camp is a cons])icuous red cinder cone 

 about 1,000 feet in height, known as Ked Cone. In zone position it is 

 well within the lower part of the Canadian belt where it is surrounded 

 by the forest of Shasta iirs, scattered trees of which push up on the 

 basal slojies and on the south side reach the top. Just below the sum- 

 mit are a few silver pines belonging to the same zone. The warm south- 

 west slope brings up Irom the Transition zone below thickets of man- 

 zanita, a few incense cedars, and several humbler plants. The cold 

 northeast slope, although reaching an altitude of only about (5,800 feet, 

 which would place it in the middle of the Canadian zone, is cold enough 

 to bring down from the Hudsonian zone several characteristic i)lants, 

 such as Polygonion neirberryi, Oymopterus terebinthinus, Cycladenia 

 humilis, IJriogonum polypodum, and Viola purpurea. 



On the south side of Shasta an interrupted ridge or series of buttes, 

 known collectively as 'Gray Butte,' reaches up the mountain side from 

 Red Cone, east of Wagon Camp, northward to the gap known as 'The 

 Gate.' In a gulch or canyon on the east side of this butte the black 

 alpine hendock descends more than 1,000 feet below its usual lower 

 limit. The reason is obvious. The row of buttes cuts off the warm 

 afternoon sun, and seepage from melting snows keeps the soil moister 

 than in more exposed places, so that the gulch meets the two require- 

 ments of the alpine hemlock — a moist soil and a cold atmosi)here. For 

 its entire length this long tongue of hemlock is Hanked by Shasta firs 

 21753— No. IC 7 



