649 
9 SE 
il*4* 
Fig. 5 
A typical cut section showing horizon of calcrete 
in Indian desert. 
Fig. 6 
Specimens of hard variety of calcrete 
Fig. 7 
Stereopair showing interdunal sandy plain of 
calcrete bearing areas in Indian desert. 
Fig. 8 
Stereopair showing interdunal hollow depressions 
having calcrete deposits in part of North East 
Nigeria. 
(ii) Though the location of calcrete and delinea 
tion & classification of soils for engineering 
purposes can be carried out through the 
aerial photographs, certain amount of field 
verification is desirable to avoid any 
discripancy or anomaly. 
(iii) The air photo patterns developed for the 
identification and location of calcrete 
bearing areas have their applicability and 
future scope not only in the terrains studied 
but also in other developing countries where 
calcareous deposits exist in similar topo 
graphical and physiographical environment. 
of 13,000 km2. 
of the site con- 
>ical stereopair 
! terrain 
study for the 
i out in the 
!Bomo and 
)00 km?. The 
•preted to be 
sllow depres- 
signs of wind 
ttion, as it has 
been the case in India. However, another prominent 
landform encountered in the region is interdunal 
hollow. These are characterised by whitish grey 
tone without land use aspect. A typical stereopair 
is shown in Fig. 8. On ground verification, the 
occuracy of interpretation has been found to be of 
the order of 90%. 
5. CONCLUSIONS 
(i) Air photo interpretation provides an accurate 
and expeditious means of conducting survey of 
highway material resources, even if the 
region is inaccessible. 
(iv) Both SLAR and Landsat imageries studied have 
depicted synoptic view of large areas of sand 
dune ridges and long narrow depressions, 
thereby providing some clue about the calcrete 
bearing landform. However, they lack 3 - 
Dimensional view of the terrain which is 
essential for the interpretation of sub—surface 
calcrete. 
ACKNOWLEDGEMENT 
The paper is presented with the permission of Dr. A. 
0. Madedor, Director Nigerian Building & Road Research 
Institute (N. B. R. R. I.) Lagos. The Author is 
thankful to him for his keen interest in the study 
and valuable discussions.