Grand Erg Oriental follow the wind's direction. There are other types of dunes, as well as "complex" dunes. Saharan winds are also known to clear an area of sand altogether, leaving bare rock (hamada) or gravel (reg). The "Grand Erg Oriental" is accessible overland by an Algerian road, which goes south from Constantine. It passes through the Aurès mountains, then salt lakes by the city of Biskra. Next the road skirts the western edge of the erg. After about 500 km. in all, it reaches the ancient oasis of Ourgla [Wargla]. Since late antiquity Wargla was a stop for the Saharan trade, being
Arabic nouns and adjectives to ones ending in , with the masculine and feminine ' being used as adjectival forms of the concept-noun (e.g. ) depending on agreement. Thus the feminine ' of ' "partnership, cooperation, participation (definite)", ' is the Arabic word for "socialism," and the word "socialist" (both as an adjective and as the term for one who believes in socialism) is ' in the masculine and "" in the feminine. The Arabic has given rise to English adjectives of nationality for Arabic countries: Iraq"i" (from ), Kuwait"i" (from ), etc. Every verb has associated active and passive participles, as well as