SECONDARY ROCKS, 
Us 
corded by travellers, is the following by Mr Bar- 
row, where coal was found at the Tyger-berg, in 
the country to the north of the Cape of Good 
Hope. It is described as a bed of imperfect coal 
resting upon clay, and covered with clay and 
white sandstone. The coal is ligneous, or of the 
nature of brown coal, and contains intermixed 
iron pyrites, and is probably an alluvial forma- 
tion. 
6. Trap. 
Trap rocks of the nature of basalt occur in 
some places in the Atlas range, apparently con- 
nected with limestone : rocks of the same descrip- 
tion are met with at Sierra Leone, and abundant- 
ly in the limestone hills of Harutsch in Fezzan* 
The limestone hills that extend from Fezzan 
to Tripoli also contain extensive formations of 
trap 5 and it is remarked, that these rocks occasion 
considerable variety in the position of the lime- 
stone strata ; owing to the crystallization of the 
trap rocks, if they are of aquatic formation, or 
to the action of the lava, if they are of volcanic 
origin. 
Detached hills of amygdaloid, also a trap rock, 
are found near the clay slate of Gellbock, in 
Southern Africa, and veins of greenstone traverse 
granite in the peninsula of the Cape of Good 
