Sandstones ferruginous

The Nubian sedimentary formation has a different origin than the Nile sediments, and the two types of sediments can be easily distinguished on the basis of trace element contents (4). As Figure 1 shows, these ancient variegated shales and ferrugineous sandstone beds are exposed in parts of the low desert surface west of the cultivation zone, as well as in the high desert areas that border the Great Wadi. 

Throughout the areas studied we observe in rocks of different granulometry, from sandstones to rocks of the terrigenous-chemical complex, primary clay mineral associations. The main components of the associations are a number of varieties of Mg-chlorites, primary hydromicas grouped together under the term ferruginous illites, trioctahedral swelling minerals and mixed-layer clays. 

In the cement of the Saharan sandstones the residual ferruginous sandstones exhibit a wide spread of from -io%o to +6%o, values which agree with those of Irwin et al. 

A magnetometer also may be used for mapping geological structures. For example, in some thick sedimentary sequences, it is sometimes possible to delineate the major structural features because the succession includes magnetic horizons. These may be ferruginous sandstones or shales, tuffs or basic lava flows. In such circumstances, anticlines produce positive and... 

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