摘要:

Foreword—The Terlingua Quicksilver Mining District in the Big Bend of the Rio Grande in southwestern Texas (Fig. 1) contains numerous small intrusive masses of diverse shapes and compositions. Some of these have approximately the characteristics of sphenoliths as defined by C. Burckhardt (Géologie de la Sierra de Mazapil et Santa Rosa, Guide des excursions du X Congres Géologique International, Mexico, 1906, Part 26, pp. 33–36, 1906). They are roughly sill‐like bodies which are irregularly wedge‐shaped and appear to have made way for themselves in part by pushing aside the strata encountered. The intrusion of this character which forms Study Butte in the eastern part of the Terlingua District has been penetrated by extensive mine‐workings, which give exceptional opportunity for study. The data on which the following description of the intrusion is based were obtained from studies of the accessible parts of the mine‐workings coupled with plane‐table mapping of the surface. The records of a number of diamond‐drill holes gave information as to parts of the intrusive mass not yet reached in mining. The examination was made as part of an investigation of the Terlingua District carried out in 1934 for the United States Geological Survey with funds allotted by the Public Wor

ISSN:0002-8606    

DOI:10.1029/TR018i001p00255

年代:1937

数据来源: WILEY

摘要:

The La Plata Mountains, in southwestern Colorado, have long been known as an example of a mountain group of the laccolithic type, although it has been recognized that the igneous geology was much more complex than that of typical laccoliths. A restudy of the ore‐deposits of the District, now in progress, has thrown new light on the mode of intrusion of the igneous rocks (E. B. Eckel, Resurvey of the geology and ore‐deposits of the La Plata Mining District, Colorado, Proc. Colorado Sci. Soc, v. 13, No. 9, pp. 508–546, 1936).The Mountains, which include parts of La Plata and Montezuma Counties, are 8 to 18 miles northwest of Durango and occupy an oval area 10 to 15 miles in diameter. The altitude ranges from about 8000 to 13,225 feet above sea

ISSN:0002-8606    

DOI:10.1029/TR018i001p00258

年代:1937

数据来源: WILEY

摘要:

The Chelmsford granite is quarried in and around Oak Hill, about six miles west of Lowell, Massachusetts. The granite‐area is about eight miles long and one to three miles wide, and its longer dimension has a northeast bearing which is parallel with the regional axis of foliation in the country rock. The writer favors a hypothesis that much of the granite represents granitization of biotite schist under hydro‐magmatic invasion, and under stress that was insufficient to deform or distort the preexisting country rock‐structures to any marked degree. Banding of the granite is due chiefly, to variable amounts of biotite. The bands are thin and remarkably uniform. The banding, attitudes of schist inclusions, and distribution of the entire mass con form to the regional structural elements. Lit‐par‐lit injection‐bands are not clearly discernible although many of the light‐colored bands are doubtless of such origin. The absence of flow‐schlieren is noted. Petrographic evidence shows a remarkable amount of metasomatic fabric. Undoubted primary granitic texture is practically wanting. There is a high degree of orientation of biotite, muscovite, and groups of small mosaic quartz‐grains. The contacts of inclusions with adjacent granite‐bands are very irregular and interpenetrative, and granitic material also penetrates intricately along schistosity planes within the inclusions. Large irregular feldspar porphyroblasts and strings of such grains are distributed through the inclusions, generally with decreasing concentration toward the centers. Pegmatite and quartz veins, some of which carry much tourmaline, are abundant in some of the quarries. Crystallization zoning of feldspars is very rare. Feldspars are of three generations: (1) Early polysynthetically twinned porphyroblasts and irregular groundmass grains of oligoclase or albite‐oligoclase; (2) microcline and orthoclase, chiefly as porphyroblasts, and in part replacing the earlier plagioclase; and (3) albite and albite‐oligoclase, untwinned and mottled, as individual crystals, streaks, patches, and porphyroblasts, replacing microcline, quartz, and mica. Incomplete twinning, corrosion‐contacts, optical anomalies, inclusions of minerals, pseudo‐perthitic and myrmekitlc grains are among the diagnostic petrographic features that contribute t

ISSN:0002-8606    

DOI:10.1029/TR018i001p00260

年代:1937

数据来源: WILEY

摘要:

The hydrated‐calcium silicates are of particular geological interest as typical minerals formed by hydrothermal reactions at contact‐zones of different mineral species. They are also of technical significance as compounds which may be formed in the steam‐treatment of Portland cement and pozzolanic materials and in the manufacture of sand‐lime brick. To ascertain which of the hydrated‐calcium silicates reported in the literature are distinct minerals. X‐ray diffraction‐patterns have been made on samples obtained mostly from the United States National Museum. Patterns were also made on the following anhydrous calcium silicates: Wollastonite, pseudo‐wollastonite, beta‐ and gamma‐ di‐calcium silicates, tricalcium disilicate, and tricalcium silicate. The other phase of the investigation now in progress, and on which this paper is a preliminary report, is an attempt to synthesize some of the hydrated‐calcium silicates

ISSN:0002-8606    

DOI:10.1029/TR018i001p00261

年代:1937

数据来源: WILEY

摘要:

A historical review, of the development of the dome of Santa Maria was presented. Dome‐building began in 1922 and continued actively for a period of three years. The dome attained during this time a height of approximately 2500 feet. Since 1925 its height has remained fairly constant but its diameter is increasing by accretions brought about by intermittent activity in various parts of the edifice. This activity is occasionally accompanied by eruption

ISSN:0002-8606    

DOI:10.1029/TR018i001p00262

年代:1937

数据来源: WILEY

摘要:

The manuscript for this paper was not submitted.

ISSN:0002-8606    

DOI:10.1029/TR018i001p00263-4

年代:1937

数据来源: WILEY