File:The continent we live on (1961) (20496691050).jpg

Title: The continent we live on
Identifier: continentweliveo00sandrich (find matches)
Year: 1961 (1960s)
Authors: Sanderson, Ivan Terence, 1911-1973
Subjects: Physical geography; Natural history
Publisher: New York : Random House
Contributing Library: New College of California
Digitizing Sponsor: Internet Archive

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positions of what is called "biotopo>;raphy" or the forminj; of land surfaces by animals, for he demonstrates that these thou sands of square miles of mounds were all built by the small, burrowinj; rodents called poc-ket gophers The method they use in digginji; and the result this has on certain types of terrain alone seem capable of producing these mounds. Dr. Scheffer produces evidence that these animals had been at work wherever such mounds are found, but he cautions that the exact method of their construction has never yet been observed in action—by pocket gophers or any other agency, biotic or physi- cal. It seems, however, that in areas where the subsoil is very firmly compacted or very rocky, or where the surface soil lies on rock, these mounds appear. It is assumed that the animals bur- row down as far as they can and throw the detritus up out of their holes Then as they extend galleries radially underground, they cause a hollow in the soil but a low dome above it, each animal family working a limited area. Rain water then collects in the gutters between these areas, while different plants grow on the slopes of the mounds and on top of them; so that by addition of soil on top and by washing away at the bottom, they form these domes, which are on an average about six feet high at the middle. FROM ALPS TO DESERTS These prairies are, as I mentioned above, ringed by a ribbon of parkland, and this in turn closes up so that the trees form a closed-canopy temperate woodland as you go up the sides of the encircling mountains. Then, if you continue upward, the com- position of this deciduous forest changes and the conifers begin to appear, while the hardwoods thin out. Eventually one enters the pure northern coniferous forest with all its belts (as seen at sea level as one travels north) neatly arranged horizontally in zones one above the other. On the higher peaks the spruces open out just as they do at the southern edge of the Arctic tundra. and true montane tundra appears in the form of tiny dwarf willows, mosses, and all the rest, to form a zone that has been locally called the "Hudsonian." Above this the tundra creeps up near the peaks but finally gives way to true barren ground with nothing but lichens. There is no better place in the world to see for yourself the rigid zoning of vegetational types and the invariable succession of these belts. Moreover, if you start your ascent up the Sierra Nevada from the Sacramento valley near its southern end, you will pass through all the major belts found on this continent north of the Mexican border. Though this province is by no means the largest on the con- tinent it is. apart from Mexico, by far the most varied. To de- scribe it as a whole requires two separate expositions. First is that of its "basis." whidi is to say its lowlands as they may be seen today and as they would cover the whole of the area if the mountain ranges were not present. Second, the mountain ranges have to be described: but these are all so different that they cannot be treated as a whole. The best procedure, therefore, is to start at the north end of the coastal string, proceed south to the San Bias, and then come back up the inland diain. This has the added advantage of leading us back up to the appropriate edge of the next province to be discussed. We may therefore begin with the Olympic Peninsula. This, as we have seen, contains a central mountain range of A mule deer fawn pauses at the foot of a great Silka Spruce in the upper montane forest of the Sierra Nevada.
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