ORDOVICIAN 



OREGON 



635 



are made on the 6-inch niaps in the parts of the 

 country where these exist, but the results are 

 published on the 1-inch scale only, except some 

 of the mineral districts, which are issued also on 

 the 6-inch scale. Besides the maps, sheets of 

 sections, horizontal and vertical, with valuable 

 memoirs, and monographs on fossils, are also pub- 

 lished ; and a general index map, scale 4 miles to 

 an inch, is in progress. A survey of the West 

 Indies has been carried ont, and memoirs descrip- 

 tive of the geology of Trinidad, Jamaica, and 

 British Guiana have been published. The geologi- 

 cal survey of Canada and that of India are vast 

 undertakings in progress ; also government geo- 

 logical and mining surveys are in progress in 

 the Australian colonies. See the articles CON- 

 TOUR LINES, MAP, SURVEYING ; Colonel White's 

 Ordnance Survey of the United Kingdom (Edin. 

 1886). 



Ordovician, a name sometimes given to a 

 geological formation intermediate between Cam- 

 brian and Silurian ; otherwise accounted the Lower 

 Silurian strata. It is so called from the Ordovices, 

 an ancient British tribe. 



Ore-deposits. Any mineral which is obtained 

 by mining, and which contains a workable pro- 

 portion of a metal, is called by miners an ore. 

 Ores are met with in various forms and positions 

 in the earth's crust. Sometimes they are found 

 in gravel, sand, and other alluvial deposits. 

 Examples of this class are afforded by the placers 

 of Canfornia (see GOLD), the now exhausted tin- 

 stream works of Cornwall, and the Img iron ores 

 of various localities. In other cases the ores occur 

 disseminated through igneous and sedimentary 

 rocks. Tin ore and magnetic iron ore are fre- 

 quently met with in this form. When the whole 

 rock is permeated with mineral matter, accumu- 

 lated in minute veins, the deposit is termed a stock- 

 work. Examples of such deposits of tin ore occur 

 at Carclase and other places in Cornwall, and at 

 Altenberg in Saxony. Again, the ores may occur 

 in detached masses. Such, for instance, are the 

 red hrematite deposits of Ul version in Lancashire, 

 the brown luematite of the Forest of Dean, the iron 

 mountains of Gellivara and Taberg in Sweden, 

 and of Missouri. The ores may occur in regular 

 parallel beds (see MINING) or seams interpolated 

 between rocks of sedimentary origin, as in the case 

 of the ironstone of the coal-measures, and in that 

 of the cupriferous shale of Mansfeld in Prussian 

 Saxony, a seam not more than 5 inches thick which 

 has been worked without interruption since the 

 12th century. Lastly, ores are met with in tabular 

 masses, known as mineral veins or lodes, differing 

 in character from the enclosing rocks. The simplest 

 classification of ore-deposits is that based on their 

 form, into two divisions: (1) tabular deposits, a 

 class subdivided into (a) beds, whether inter- 

 stratified or superficial, and (b) lodes; and (2) non- 

 tabular deposits, or masses. 



A lode is usually defined as a repository of 

 mineral matter which fills more or less completely 

 a former fissure. Though this definition is un- 

 doubtedly true in most cases, deposits are occasion- 

 ally met with in which the rock at the sides of the 

 fissure, having been so altered as to render it worth 

 working, should be considered as part of the lode. 

 These exceptional cases are included in a more 

 general definition propounded by Dr C. Le Neve 

 Foster, who regards lodes as tabular deposits of 

 mineral, which have been formed subsequently to 

 the rocks by which they are surrounded. Lodes 

 are very variable in thickness, from a mere film up 

 to 150 feet or more. Their longitudinal extent is 

 equally variable. The (Treat Mother Lode of Cali- 

 fornia lias been traced lor a distance of 70 miles. 



In tabular deposits, whether beds or lodes, two 

 dimensions predominate, and the third or smallest 

 dimension, the perpendicular distance between the 

 two bounding planes, is termed the thickness. 

 The adjacent rock on both sides of these two planes 

 is termed the country ; the portion on which the 

 deposit lies is the foot-wall, and that covering it is 

 the hanging-wall. With beds or seams, these are 

 known as the floor or roof respectively. The strike 

 of a deposit is the angle formed with the meridian 

 by the direction of a horizontal line drawn in the 

 middle plane, and its dip is the inclination down- 

 wards measured in degrees from the horizontal. 

 As the dip of lodes is usually considerable, it is 

 sometimes measured from the vertical, and is then 

 termed underlie or hade. The portion of a mineral 

 deposit occurring at the surface is known as the 

 outcrop, basset, or (in the United States) apex. 

 The contents of lodes vary, some parts containing 

 worthless vein-matter or gangue, others being filled 

 with ore. The productive portions are termed 

 courses, bunches, shoots (U.S. chutes), or pipes of 

 ore. Cross-courses are veins with a direction nearly 

 at right angles to the chief lodes of any particular 

 mining district. Experience shows that the pro- 

 ductiveness of lodes is affected by intersection with 

 other veins, by the nature of the adjacent rock, and 

 by changes of dip or of strike. 



The origin of mineral veins is a much debated 

 subject wTiich has long occupied the attention of 

 geologists. All the theories which have at various 

 times been brought forward assume in the first 

 place that a fissure has been formed in the earth's 

 crust. This fissure has, it is thought, been filled 

 up by mechanical action ca'using the attrition of 

 the sides, by sublimation, by injection of molten or 

 plastic material from below, as in the case of dykes 

 of eruptive rock, or, lastly, by depositions from 

 solution, coming from above, from below, or from 

 the sides. The last mentioned, known as the 

 lateral secretion theory, has received great sup- 

 port by the researches of Prof. F. Sandberger. 

 These researches have shown the presence of the 

 common heavy metals in rocks belonging to every 

 geological period. Copper, tin, lead, zinc, cobalt, 

 and nickel have been detected in silicates (mica, 

 augite, and olivine), occurring as component 

 minerals of the commonest rocks. Prof. Sand- 

 berger therefore concludes that these metals have 

 been dissolved out and deposited in fissures. 



The subject of mineral deposits is systematically 

 treated in J. A. Phillips' Treatise on Ore-deposits 

 (Lond. 1884), in which a full bibliography of the 

 subject will be found. The reduction of ores is 

 discussed under METALLURGY, and under the names 

 of the several metals. 



Or'egon, a Pacific state of the American Union, 

 bounded N. by Washington, E. by Idaho, S. by 

 California and Nevada, and W. 

 by the Pacific. Lat. 42 46 

 N., long. 116 40124 45' W. 

 Area, 96,030 sq. m. , or almost twice that of England. 

 Oregon on the west is literally rock-bound by 

 the Coast Range of mountains, having, however, 

 numerous indentations which furnish good harbours 

 for sea-going vessels. The Columbia River affords 

 the largest and deepest entrance. Seventy miles 

 east of the Coast Range is the Cascade Range, 

 rising to a height of 6000 to 8000 feet, and at 

 almost regular intervals surmounted by snow- 

 capped peaKS of nearly double that altitude. From 

 the Cascade Range eastward to the Blue Moun- 

 tains, about 70 miles, and farther on to the eastern 

 boundary of the state, the surface is diversified by 

 mountains and valleys, rolling plains, and table- 

 lands. Here the soil and climate are suitable for 

 agriculture and grazing. In Western Oregon is 

 the Willamette valley, 130 miles long and 60 miles 



Copyright 1891, 1897, .111,1 

 1900 hi the U.S. by J. B. 

 Llpplncott Company. 



