Prilog proučavanju silikatnog krasa Sahare

Silicate sandstones of Paleozoic age are very widespread in Sahara. In these were formed numerous caves and other relief forms, proper to the karst. In order to establish the genesis of these forms, a series of laboratory experiments have been made on the sandstone samples. The samples originate from the oasis Bardai (Tibesti, Chad), and also from a locality called Tamega, north of the border crossing In Guezzam (Algeria). By Bardai-sandstone has been analyzed the compact rock (test 1), the dust from decomposition, scraped oft from the rock (test 2) and the dust from the 'Quatre roches' foothill (test 3), and by Tamega-sandstone the compact rock (test 4) and dust from decomposition, scraped off from the rock (test 5). The rock samples were first reduced to dust, the size of its corns being under 0,5 mm. After that, from each sample were taken 5 g and put into a laboratory cup of quartz glass in which there already were 2 l distilled water. At the temperature of 21-22.5 the pump blew continually for 15 days air into water with a view to forming H2C03 more rapidly and possibly to dissolving mineral matter. In parallel with this proceeding, there was established the quantity and chemical structure of cement in all the samples (Tab. 2). This was done by dissolving the pulverized sample in boiling distilled water, which was chemically analyzed after that. In the first experiment, concentrations of individual elements after 24 hours of dissolving reached already 50-70% of values obtained after 15 days of dissolving (Tab. 1). This points out that the process of dissolving and of chemical modification of mineral substance is comparatively rapid and that it depends more on the quantity of fresh water and on the temperature, than on the length of contact between water and rock. It was established further, that (lie disintegration of analyzed sandstones occurs chiefly on account of the transition of calcium, sodium and potassium from cement into the water solution. Although the grains of quartz in sandstones constituted over 95% of the rock mass, in water were found very small quantities of dissolved silicates - negligible in comparison with other chemical components. Microscopic analysis of the Tamega-sandstones, which are of Ordovician age, it turned out that the quartz grains in them were exposed to the processed of metamorphism and even before their sedimentation, owing to transport, partly processed. Consequently, there are no proofs that the 'corrosive' changes on the quartz grains, which were observed by some investigators, are in relation with geomorphologic processes which have led to the creation of forms of silicate karst. On the basis of the executed laboratory experiments, one came to the conclusion that the forms of silicate karst are polygenetic and only morphologically similar to the forms of relief which are formed in limestone, dolostone and gypsum

Uporedna analiza pronosa suspendovanog i hemijskog nanosa u slivovima Belog i Crnog Timoka

The river basins of the White Timok and the Black Timok are situated in East Serbia. Petrologically they differ very much from each another: in the river basin of the Black Timok (1,199 sq km) there predominate limestones (39%) and andesites (34%); in the upper part of the river basin of the White Timok (1,245 sq km) magmatic-metamorphic rocks (60.4%), and in its lower part (905 sq km) maritime-lacustrine sediments (36%). As the above mentioned river basins differ from one another also from hydrological point of view, the object of this paper was to establish the total evacuation of suspended and chemically dissolved deposits, as well as its structure. The greatest evacuation of deposits is in the very liver basin of the White Timok (224,8 t/km^2/year), and the least one in the river basin of the Black Timok (68,7 t/km^2/year). These two river basins basically differ from each other also by the structure of evacuated materials: in the former there predominates silt (82,8%), and in the latter chemically dissolved matters (94,9%). On the basis of relations, in which E is the sum of evacuations of suspended and chemically dissolved deposits (mg/km^2/s and q specifical flow-off (1/s/ km^2), it can be concluded that for the same abundance of water the immediate part of the water basin of the White Timok is 8,3 times ämore credible' than the river basin of the Black Timok

Problemi razvoja i razmeštaja industrije u planinskim predelima Srbije

In the paper is emphasized that the environment reflexes on the economic matrix disproportion and anomalies in the industry because of the specific mountains conditions. It is necessary to work our in detail the convenient politics for the development of industry in the mountain region in Serbia. The social, economic and political reforms have to contribute to the decentralization of production and management, which will create favorable conditions for the industrial development and the total development of the mountain regions of Serbia

Istorijsko-geografski pregled poznavanja pecina u Srbiji pre XX veka

An account of publications and authors who wrote about caves in Serbia before the 20th century is given. These are: Evlija Celebija, Joakim Vujic, O.O.Pirh, Ami Boue, Josif Pancic, Feliks Kanic, S.St.Riznic, Vladimir Karic, Jovan Zujovic, D.P.Jovanovic and M.Zivkovic. The best articles describing the caves of E Serbia were written by Jovan Cvijic. -Bull. Sci. Sect. B Yougosl