Vol. 55.] SOUTHERN MOROCCO A^STD THE ATLAS MOUNTAINS. 195 



in no wise be formed by the ordinary action of surface-streams. 

 These lowland areas, in fact, represent a Tertiary sea-bottom, 

 raised above the water exactly as it was formed. It might have 

 been supposed that all its characteristic features would have been 

 obliterated during the long ages which have elapsed between its 

 first appearance above water and the present day. The survival of 

 these features, without a doubt, is due to the porous character of the 

 shell-sands, permitting the absorption of the rainfall, and preventing 

 the formation of streams and rivulets. Over large districts, however, 

 the subaerial denudation of the country has been prevented in a 

 totally different manner — namely, by the formation of a slag-like 

 calcareous crust of extreme hardness, which practically seals up 

 the ground and defies equally the operations of the husbandman 

 and the weathering agencies of nature. 



The natives take advantage of the occurrence of this slaggy crust 

 over an easily-excavated rock to dig their underground granaries 

 and reservoirs. Its origin is ascribed by ]Maw,^ and I believe 

 correctly, to the rapid evaporation of waters charged with soluble 

 carbonate of lime by the intense heat of the sun. The residual 

 carbonate is deposited layer by Isijei on the surface. He speaks 

 of it forming accumulations in this manner several feet thick ; but 

 on that point I am disposed to think that he must be mistaken, 

 and that he has confounded the surface-soil and upper layers of 

 rock cemented into a more compact mass by the precipitated car- 

 bonate with the actual deposit of calcareous crust itself. In any 

 case, I have never seen any such deposit thicker than a couple of 

 inches, while I have fi'equently observed the surface-layers of a 

 porous rock as well as sand cemented by the deposition of new 

 matter into a marble-like compactness. 



It would be difiicult to say what thickness these Tertiary shell- 

 sands reach, but it is probably in places 200 or 300 feet. At one 

 locality, south of Saffi, our Yice-Consul, Mr. Hunot, sank a well 

 for a depth of more than 100 feet, before reaching a white 

 lithographic stone ; and a section exceeding 200 feet in thickness 

 is shown at the Jews' Cliff, a few miles south of Saffi. At the 

 last-named locality, Miocene beds are seen cropping out from beneath 

 others of Pliocene date, and dipping at a considerable angle north- 

 westward. Underneath, at the base of the cliff, are Cretaceous red 

 and grey marls, and a white sandstone. 



Among the most interesting phenomena, however, observable 

 in the Tertiary deposits near Saffi are several quarry-like holes in 

 the shell-rock. One of these may be found close to Mr. Hunot's 

 farm, and another immediately behind the Jews' Cliff. At a 

 cursory glance, one would naturally assume them to be what they 

 seem, namely, quarries, until a more careful examination shows that 

 the rock is not such as is used for building, and that if they have 

 been used as quarries they have been worked in a very unusual 

 and peculiar manner. 



On the other hand, the inhabitants themselves look upon these 



1 [OjJ. cii. p. 455.] 



o2 



