The Pliocene appears only in the coast region of the Black and Azov Seas, but it is widely developed in the Aral-Caspian region, where, however, the Ust-Urt and the Obshchiy Syrt rose above the sea.
The second-class fortresses are Kronstadt and Sveaborg in the Gulf of Finland, Ivangorod in Poland, Libau on the Baltic Sea, Kerch on the Black Sea and Vladivostok on the Pacific. In the third class are Viborg in Finland, Ossovets and Ust Dvinsk (or Dunamunde) in Lithuania, Sevastopol and Ochakov on the Black Sea, and Kars and Batum in Caucasia.
AMUR (known also as the Sakhalin-ula), a river of eastern Asia, formed by the confluence of the Argun and the Shilka, at Ust-Stryelka, in 53° 19' N.
Both these rivers come from the south-west: the Argun, or Kerulen as it is called above Lake Kulun (Dalai-nor), through which it flows about half way between its source and Ust-Stryelka, rises in 49° N.
The principal water-divide in this highland region is, however, the range of Egri-dagh (Ararat), which j ust south of 40° S.