134 ( No. 98 ECONOMIC CONDITIONS deposits, two to five miles in length , andgenerally of a distinctive oolitic character. Å bed of highly ferri ferous sandstone is reported as underlyinga great mass of intrusive basalt or dolerite in the Jebel Alarainbia , near Kerma , in the Dongola province . In the Bahr el-Ghazal , Mongalla, and Upper Nile provinces , the rocks are generally covered by a ferruginous con glomerate associated with a lateritic formation . The rivers and streams expose it admirably , and in places between Rumbek and Mvolo, for instance, the thick ness is as much as 50 ft. Usually, the surface con sists of red loamy soil strewn with boulders of different sizes , and supporting a dense growth of forest and grass. In places, however, the ferruginous conglomerate forms isolated patches of considerable size, so bare of soil that only a scanty supply of short grass succeeds in growing. In the Bahr el-Ghazal province alone, the iron ores cover an area of nearly 31,000 square miles , of which the thickness varies from 3 to 16 ft . , but may be much greater in places .

The blackening of rocks is a peculiar feature of the conditions obtaining in the arid regions of the northern Sudan . . This appears to be due to the presence of moisture, which brings the iron to the surface and deposits it there on evaporation . In areas formed of Nubian sandstone , this chemical action produces a crust which extends over wide areas , but is seldom more than a few inches in thickness . Many travellers have been misled by the appearance of these crusts, andhave described the rocks as volcanic . The existence of this peculiar surface action renders it difficult to differen tiate the inter -stratified ores from the crust .

In the south and west of the Sudan , the natives have for many years smelted iron , utilising charcoal and clay furnaces about 3 ft . high, with portable goat -skin bellows. Soft iron, apparently of very good quality, is produced, and is distributed among the natives all over the Sudan in the formof weapons, tools, and ornaments . The principal tribes at present engaged in smelting and smith-work are the Jur, around