occupy canyons eroded to a considerable depth. “ It is quite possible, therefore, that volcanic activity may have been initiated either early in Glacial time or prior to the onset <strong>of</strong> glaciation. The evidence at hand seems to indicate that the volcano was active up to some time within the last few hundred years; and it may still be merely dormant rather than extinct.“* Near Atlin olivine basalt and related pyroclastic rocks form the cone <strong>of</strong> Ruby Mountain west <strong>of</strong> Ruby Creek, and some lava has flowed down the creek almost to Surprise Lake. This lava, partly post-Pleistocene in age, consists <strong>of</strong> thin olivine basalt flows, each 5 to 15 feet thick and totalling about 120 feet in thickness. The lava lies above gold-bearing gravels and forms a canyon along the creek. Two fans <strong>of</strong> scoriaceous material on the west side <strong>of</strong> the creek evidently represent the latest outpouring from the Ruby Mountain cone. On the east side <strong>of</strong> Ruby Creek there is one small cinder cone. These occurrences occupy a small area and are the northernmost evidence <strong>of</strong> late volcanic activity in <strong>British</strong> <strong>Columbia</strong>. [References: Aitken, J. D., “Atlin Map-area,” Geol. Surv., Canada, Mem. 307, 1959; Black, J. M., “Atlin Area,” B.C. Dept. <strong>of</strong> Mines, unpublished manu- script; Kerr, F. A., “ Lower Stikine and Western I,skut River Areas, <strong>British</strong> Colum- bia,” Geol. Surv., Canada, Man. 246, 1948; Lord, C. S., “McConnell Creek Map- area,” Mem. 251, Geol. Surv., Canada, 1948, p, 43; “ Stikine River Area,” Gal. Surv., Canada, Map 9-1957; Hanson, F. A., “ Reconnaissance between Skeena River and Stewart,” Geol. Surv., Canada, Sum. Rept., 1923, Pt. A, p. 39; Dol- mage, v., “Coast and Islands <strong>of</strong> <strong>British</strong> <strong>Columbia</strong> between Burke and Douglas Channels,” Gal. Surv., Canada, Sum. Rept., 1921, Pt. A, p. 29; Davis, N. F. G., “ Clearwater Lake Area,” Geol. Surv., Canada, Sum. Rept., 1929, Pt. A, p. 290; Mathews, W. H., “ Geology <strong>of</strong> Mount Garibaldi,” Geol. Sot., Am., Bull. Vol. 69, 1958, pp. 161-198; Mathews, W. H., “Mount Garibaldi, A Pleistocene Volcano,” Am. Jour.Sci.,Vol. 250, 1952, pp. X1-103; Watson, K. Dep., andMathews, W. H., “ The Tuya-Teslin Area,” B.C. Dept. <strong>of</strong> Mines, Bull. No. 19, 1944; Cotton, C. A., “ Volcanoes as Landscape Forms,” Whitcombe and Tombs, Ltd., Christchurch, 1952.1 [Photographs: B.C. 502:6, B.C. 866:34,49; B.C. 984:59, 64; B.C. 985:26; B.C. 986:90; B.C. 1374:28; B.C. 1744:lO; B.C. 1919:38.] MAJOR LINEAMENTS OF BRITISH COLUMBIA Lineaments are extremely common features in the landscape <strong>of</strong> <strong>British</strong> Colum- bia. They are normally on so large a scale, however, that they may be difficult to recognize on the ground. Many have lengths measured in scores <strong>of</strong> miles, and consequently are most frequently discovered through study <strong>of</strong> topographic maps (see N.T.S. Sheets 92iv and 103~) or aerial photographs (see Plate XLVIII), or by direct observation from an aircraft in flight. A lineament is an alignment <strong>of</strong> topographic features that is structurally con- trolled; that is, it is governed by or directly related to some geologic structure. It may consist <strong>of</strong> some straight or gently curved topographic feature, such as an alignment <strong>of</strong> valleys, wind gaps, scarps, or ridges, whose origin is controlled by faults, joints, bedding, geologic contacts, foliation, or 1ineation.t Drumlins and glacial flutings are not lineaments because, although they may be strongly linear in their arrange- ment, they are not structurally controlled. Few studies <strong>of</strong> lineaments in <strong>British</strong> <strong>Columbia</strong> have been made, and no pub- lished results are available. However, their study and investigation is useful. par- * Kerr, P. A., Ged. surv., Canada, Men. 246, 1948, p. 4% + Billings, M. P., “ SfmCtwal Geology.” Prentice HO,,, NW York, 1954, p. 160. 120 , J
‘I , titularly for those interested in the structure <strong>of</strong> areas for which geologic maps are inadequate or lacking.* It is possible to point out the occurrence <strong>of</strong> numerous lineaments, but owing to deficiencies in geological information it is not always pos- sible to interpret their structural significance correctly. Figure 12. Diagram showing the location <strong>of</strong> major lineaments. Figure 12 shows the locations and lengths <strong>of</strong> the major lineaments whose descriptions follow. By far the longest and most prominent lineament in the Province is the Rocky Mountain Trench ( 1) t (see Plates XXII, XXIVA, and XXXIVB) . It extends along the western front <strong>of</strong> the Rocky Mountains in a northwesterly direction for 900 miles, from the International Boundary almost to the Liard River (see p. 65). The struc- tures controlling the Trench are complex, variable from section to section, and not very well known. “ In certain areas the dominant controlling structure is thrust faulting, whereas in other areas it is normal faulting, and in still others strike-slip faulting is indicated. Although the type <strong>of</strong> faulting varies, there is no area that has been investigated along the Trench in which faults are not observed or required by the relationships on either side. If this is true <strong>of</strong> the unmapped areas as well, then a linear zone <strong>of</strong> faulting about 1,000 miles long is indicated. Individual faults within this zone may control the structural relationships and the position <strong>of</strong> the Trench locally, but the gross shape and regional structural relationships are controlled by the zone <strong>of</strong> faulting as a whole.“$
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Bulletin 48 Landforms of British Co
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The technical references are believ
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PAGE Chapter II.-Physiographic Subd
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FIQ. ILLUSTRATIONS 1. Landform map
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PLATE PAOE XVIII. (33) Stikine Plat
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PLATE XXXVIIB. (70) Rocky Mountain
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traveller. If he SO wishes, his enj
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pendants which, because of their se
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As Iava cools and consolidates, it
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are lithologic differences from pla
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mentary rocks are folded and faulte
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Field work by members of the Geolog
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BIBLIOGRAPHY Alden, W. C.: “ Phys
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The western boundary of the Eastern
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INSULAR MOUNTAINS The Insular Mount
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H. C., “ Geology and Mineral Depo
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The extreme northeastern tip of Gra
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the strait. It is suggested that th
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The lowland consists of many low, w
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anges farther west. The ranges sout
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Pacific Ranges The Pa&c Ranges (see
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Columbia. The mountains along the 4
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ones, and widening and deepening th
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south end of Teslin Lake, which sep
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Between the Taku &nd Sheslay Rivers
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The tuyas consist of nearly horizon
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sloping areas of upland remain undi
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mostly in the Babine Range. The roc
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to Eutsuk Lake on the southern side
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I These valleys are at a fairly hig
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Detailed studies made around severa
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The area is drained by the Finlay,
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Plateau and the Nechako Plateau, an
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