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GEOLOGICAL MEMOIRS. 



12. The volcanic mountains are distinguished from the plutonic, 

 consolidated within the earth, both by their external form and by their 

 mineralogical conditions. The first form superficial, the second form 

 subterranean cones of eruption. The section of these last exhibits 

 (for example) the so frequently referred to granite-ellipsoids. Both, 

 however, fill up also narrower fissures, in which they are then mostly 

 crystallized somewhat otherwise than in the great principal masses. 



[T. R. J.] 



On some Fossils from the Lower Chalk Formation of the Cape 

 of Good Hope. By Prof. Dr. F. Krauss. 



[Nova Acta Acad. C. L. C. Nat. Cur. vol. xxii. part 2. 1850, pp. 439-464.] 



In April 1839 the author made an excursion from Uitenhage, 

 which lies near the Kaffir boundary and only a few leagues from 

 Algoa Bay, along the left bank of the Zwartkops River, as far as its 

 mouth, and met with fine sections of fossiliferous strata, probably 

 belonging to the Lower Greensand. 



In a communication made by Dr. Krauss in 1842 to the Meeting 

 of German Naturalists and Physicians at Mayence*, he made men- 

 tion of this formation, and exhibited the fossils found in it ; and in 

 this memoirf he now gives detailed descriptions of the same, illus- 

 trated by four quarto lithographed plates. 



The occurrence of this formation, says the author, is so much the 

 more remarkable, as along the whole seaboard from Table Bay % to 

 Algoa Bay, nearly through eight degrees of longitude, nowhere does 

 a trace of it occur. I have crossed this tract of the coast as far as 

 Karroo in all directions, and always found on the heights of variegated 

 sandstone, in the valleys and plains of clay-slate or greywacke-slate, 

 rare beds of a sandstone-conglomerate or intrusive granite. Even on 

 the Zwartkops River Heights, near Uitenhage, the greywacke occurs, 

 and on the neighbouring Van Stadenberg the sandstone. 



In descending, however, the bed of the above-mentioned river, we 

 are soon struck by a vegetation remarkably different from that of the 

 other districts, and still more astonished by the beds of colossal 

 Trigonice, perfect specimens of which, washed out by the water, lie 

 exposed in many places. 



As far as I could examine the extent of this basin, I found it to 

 reach from the salt-lakes between Uitenhage and Port Elizabeth, 

 along the Zwartkops River below Uitenhage, and partly on the Koega 

 River, as far as the Zondag [Sunday] River §, in a circuit of several 

 leagues. 



About one and a half league below Uitenhage I found close to the 

 left bank of Zwartkops River a very fine section of a mass of Green- 



* Amtl. Bericht, p. 126. f Communicated to the Academy in April 1847. 



% See Map of the Cape Colony, accompanying Mr. Bain's Paper on the Geo- 

 logy of the Albany District, Trans. Geol. Soc. vol. vii. PI. 2. 



§ These three rivers, running parallel with each other from N.W. to S.E., empty 

 themselves into Algoa Bay. Sunday River is the most easterly, and Zwartkops 

 River, on which Uitenhage is situated, is the most westerly. 



