In 1951, a Gobi Geological Detachment was established within the Mongolian Integrated Agricultural Expedition. Its mission was to conduct a reconnaissance survey of the Trans-Altai Gobi, a region that had not previously undergone geological investigation. The detachment consisted of Dr. V. M. Sinitsyn, a Doctor of Geological and Mineralogical Sciences, and V. A. Amantov, a graduating student of the Leningrad Mining Institute. In Ulaanbaatar, the team was expanded to include the driver A. S. Karabin, the interpreter Dashchik Sambuyev, a third-year student at the Mongolian State University, and a worker named Zhana. On June 10, the detachment departed Ulaanbaatar in an assigned ZIS-5 truck, following the ancient Gobi route through Dalandzadgad and Obotu Khural toward the study area. The Trans-Altai Gobi constitutes the southwestern part of the Mongolian People's Republic and is the region most distant from the capital. There are two routes leading into the Trans-Altai Gobi: one follows the Tsetserleg road through the Khangai Mountains, the Valley of Lakes, and the Mongolian Altai; the other follows the Dalandzadgad road across the Gobi Plateau, crossing only the outlying ranges of the Altai Mountains. The first route leads to the northwestern part of the Trans-Altai Gobi, while the second reaches its southeastern sector. The distance from Ulaanbaatar to the nearest point of the region by either route is approximately the same, about 1,300-1,350 kilometers. The Trans-Altai Gobi encompasses the eastern extremity of the Dzungarian Basin, the southern spurs of the Altai Mountains, and the Gobi extensions of the Tianshan range located within the Mongolian People's Republic. Its territory stretches northwestward, occupying the space between the trend of the Altai Mountains and the frontier with China. The eastern boundary of the Trans-Altai Gobi approximately coincides with 100°30′ E longitude, while the western boundary lies near 90°30′ E longitude. Because the territory extends toward the northwest, the southern boundary rises from 42°30′ N latitude in the east to 45°15′ N latitude in the west, while the northern boundary correspondingly shifts from 44°30′ N to 46° N (see Fig. I). As one of the inland regions of Central Asia, the Trans-Altai Gobi is renowned for its extreme desolation. The detachment encountered tremendous difficulties there, including severe water scarcity, the absence of permanent settlements, limited conditions for motor transport, great distances from fuel stations, and harsh climatic conditions characterized by exhausting heat and extreme dryness. The expedition worked in the Trans-Altai Gobi for four months. During this period, it completed 4,200 kilometers of reconnaissance geological traverses covering the area from 99° E longitude to the bend of the Bulgun River. Of this distance, 1,780 kilometers were covered by camel and on foot, while 2,420 kilometers were traversed by vehicle. The detachment completed eight full north-south crossings of the Trans-Altai Gobi, together with numerous partial traverses confined to individual tectonic-morphological regions. The reconnaissance survey covered an area of 90,000 square kilometers. A total of 890 rock specimens were collected. Fossils of flora and fauna from the Silurian, Middle and Upper Devonian, Tournaisian, Viséan, Lower Permian, and Cretaceous periods were obtained from 32 localities. Heavy-mineral concentrate samples were collected from 42 sites. Owing to the exceptionally favorable outcrop conditions characteristic of Central Asia and the availability of excellent topographic base maps at a scale of 1:200,000, we were able, despite the wide spacing of traverses, to identify the principal structural features of the Trans-Altai Gobi and to compile a geological map broadly meeting the requirements of a 1:1,000,000-scale map. After returning from the Trans-Altai Gobi, the geological detachment conducted a route survey along the railway from Ulaanbaatar to the Soviet border. At the end of October, the members of the expedition returned home. Laboratory processing and analysis were carried out at the Coal Geology Laboratory in Leningrad. Owing to delays in the delivery of field materials, we could not begin this work until the eve of the New Year. Our rock specimens, together with those collected by other sections of the agricultural expedition, were packed into a truck that was transported on an open railway flatcar. In the Irkutsk region, the truck caught fire, causing severe damage to the materials inside, including our collections. By the time the shipment arrived in Moscow, the specimens were scattered, packages had been burned, and some labels had been lost. Because duplicate samples had been reserved for thin-section preparation, losses among the petrographic collections did not exceed 30 percent. Paleontological specimens, particularly small fragments packed together in large bundles, suffered far more extensive damage. Specimens from many localities could no longer be found among the surviving collections, while those from other sites were only partially preserved. Of the heavy-mineral samples, only three survived. The laboratory processing work, which had not been covered by the expedition's budget, could only be completed in part. The funds allocated by the Mongolian Committee were far from sufficient to support the necessary volume of research. With the available resources, we prepared 300 petrographic thin sections instead of the 700 originally planned, partially covered the costs of fossil identification, and arranged for the manuscript to be printed. A number of studies originally planned, including specialized petrographic and mineralogical investigations, monographic treatment of fossil materials, silicate analyses, spectral analyses, and other related work, could not be carried out because of insufficient funding. The paleontological materials that survived the fire were examined by Academician D. V. Nalivkin; Full Member of the Academy of Sciences of the Ukrainian SSR A. N. Krishtofovich; and paleontologists L. D. Kiparisova, T. A. Aleksandri-Salova, V. N. Trizna, B. V. Nalivkin, D. F. Maslennikov, B. P. Markovsky, E. M. Lyutkevich, D. L. Stepanov, and A. M. Obut. The principal identification of the fossil collections was carried out by L. P. Monakhova. The petrographic thin sections were examined by V. A. Amantov, a participant in the field expedition. He also prepared the materials used in Chapter II of the geological overview concerning plutonic igneous rocks.