The Prone Valley is located in the middle of Kartli, to the right side of Mtkvari. It covers Dvani Tskali, Ali Tskali, Ptsa Tskali and Surami Tskali. People call these rivers Prone today tooin accordance of the historical term. The Book of Ruisi Flock or the Chronicle of Ruisi composed by Nikoloz  Mroveli Orbelishvili or Kaplanishvili in 1715 gives us the important information for diachronic study of the toponyms of this valley with regard to linguistic; Vakhusht iBagrationi’s “Description of the Kingdom of Georgia (Geography of Georgia)” (in the middle years of XVIII century); Ioane Bagrationi’s “Description of Kartl-Kakheti” (1794-1799) and the recorded and analyzed materials by the Georgian researchers (S. Makalatia, Al. GhlontI, M. Koberidze, N.Otinashvili) in different times with dialectological point of view.

Speech of villages of DvaniTskali and PtsaTskali belongs to Shidakartlianand speech of villages of Ali Tskali and SuramiTskali belongs to – Western Kartlian.

Toponyms of the Prone Valleyare various according to the content and the composition, the confirmed means of word composition are similar to Georgian literary language and other dialects of Georgian language. As substantive (martulmsazgvreliani) as attributive (atributulmsazgvreliani) micro (nakedlarebi, chakidula…), macro (Dvanistskali, Prone) and in particular toponyms (Dvani, Dirbi, Taxtidziri  ...)  occur, where occur “tskali”, “tba”, “ghele”, “tchala”, “khevi”, “tchaobi”, “morevi”as a component part of composite. With such kind of toponyms as an attribute is confirmedas common as proper nouns. For the toponyms of Prone Valleyare peculiar these phonetic processes what are peculiar for the Georgian languagesystem. For example: loss of letter, replacement of letters, insertionof letter… composition with suffixes (-et,- it, -at, -is-i, -at(a), -ta, -eul, -ul, -ur, -ovan, -osan, -in-a, -eb, -mar ( nar) and with prefix-suffixes (na-ev, sa-e, sa-ur, sa-ia). Spreading area of toponymsand frequency of formative mean create difference. Difference occasions refer to the unification tendency and the occasions of changeover of codes of speech. It is noted territorial localization of dialectical vocabulary used as toponym.    The analysed material is multifariousdue to its content. There are no borrowed terms, but all are Georgian formation.  The toponyms of “ Tskal” and “Tskhar” basis are used more frequently. The majority of toponyms are complex words. Common nouns as well as proper nouns can be the qualifiers of such types of toponyms.

Key words:Prone Valley, Toponym,  Dialect, Kartlian, Composition, Localization, Lexis.