THE seventeenth International Geological Congress is being held in Moscow on July 20-30, as noted in NATURE of January 23, p. 143. Many tours for the delegates have been arranged ; for this purpose guidebooks have been prepared giving detailed descriptions of the routes, all the interesting outcrops of mineral strata, the deposits of useful minerals, etc., with maps, plans and sectional drawings. Every delegate has a set of twenty-eight guide-books, and a newly issued geological map of the Soviet Union ; each tour is being conducted by a Soviet geologist. According to a report issued by the Soviet Union Year Book Press Service, 403 foreign delegates, representing forty-six different countries, are attending the Congress ; they include 139 from the United States, 50 from Great Britain, 33 from France, 20 from Japan and Manchukuo, 13 each from Germany and South Africa, and 11 from Sweden. Of Soviet geologists, 1,600 have intimated their desire to be present, but as many of them are at present engaged in field work, not all of them will be able to attend. The delegates will spend two days in Leningrad, where a session of the Congress will be held, and visits will be paid to the geological museums of the Mining Institute, the Central Institute of Scientific Research, the Arctic Institute, to give representatives of foreign countries an opportunity of becoming acquainted with the general characteristics of the mineral resources of the Soviet Union. In Moscow, the Congress will hold its sessions at the Observatory, where the institutes of the Academy of Sciences of the U.S.S.R. have also arranged an exhibition of collections relating to mineralogy, geochemistry and useful minerals ; and the Palæontological Institute is showing its collection of Perm vertebrates of the North Dvina Gallery. Among the subjects coming up for discussion at the Congress are: problems of oil and world oil resources ; geology of coal deposits ; the Pre-Cambrian system and its useful minerals ; the Perm system and its stratigraphical arrangement ; the inter-connexion of tectonic processes, magmatic formations and ore deposits ; tectonic and geo-chemical problems of Asia ; deposits of rare elements ; geophysical methods in geology ; geology of the Arctic and Antarctic.