07 



limestone concretions, sandy clay, &c, and besides obtain 

 less moisture, the water being collected and retained by the 

 hollows. These, therefore, exhibit a denser growth of grass 

 and herbs, and consequently an accumulation of mould. 



To account for the different inclinations which the " Bay of 

 Biscay" soil shows, an unequal, but else regular, elevation of 

 the whole area is required ; but the various inclines may also 

 have been produced by differential denudation, the latter being 

 more rapidly canned on where the soil operated on was thickest, 

 and thus the valleys scooped out between the hills ; on the sides 

 of the hills a part of the soil was left, which originally occupied 

 different levels. 



In proof of the theory advanced as to the origin of this 

 peculiar soil, a few observations will be cited. In the neigh- 

 bourhood of " Bay of Biscay" regions extensive patches of fine 

 white sand are found, generally overgrown by dense scrub ; 

 but occasionally holes are found blown out by wind, in which 

 are left all heavier ingredients. Amongst these the writer has 

 sometimes found fragments of large shells. Being 30 to 40 

 miles from the next sea-shore, their carriage thence by human 

 agency is, at least, very improbable. Whether these sands be 

 assigned to a marine or lacustrine origin is immaterial, as that 

 would not affect the final result. Underlying these sands and 

 the "Bay of Biscay" clays, are frequently found thin layers of 

 ferruginous sandstones and conglomerates, destitute of fossils 

 (except some cavities resembling those left by the removal of 

 large shells or echinids, and some fossilized wood), fringing the 

 respective regions to a great extent, they are found neither to 

 retain the same direction (part denudation), nor the same level 

 (inequality of elevation) ; never of great vertical thickness, 

 they are penetrated by numerous perpendicular smooth fissures, 

 partly filled with fine oxide of iron and small round holes, 

 through which the rainwater penetrates to the underlying beds. 

 The latter consist of gravels and sand, in some places that were 

 examined ; in others of an arenaceous clay strongly impreg- 

 nated by saline substances, impure salt forming numerous small 

 veins and nests therein. Below these again purplish ferruginous 

 shales of a peculiar wavy structure follow invariably where 

 examined near Nuriootpa, Tanunda, and Greenock. 



The latter observations were first made by the writer in 

 1S76-7, and if the saline clays should prove a general feature 

 in connection with the "Bay of Biscay" soil, their discovery 

 would reveal the cause why wells in such regions always 

 produce salt-water. The whole series rests unconformable 

 upon palaeozoic rocks of pre-silurian age. 



Having first shown, by assuming an originally level surface, 

 that the physical properties of this soil admitted and necessitated 



