22 GEOLOGICAL MEMOIRS. 



rectly, immediately afterwards it was violently disturbed by the por- 

 phyries that burst forth in many points of the Lower Silesian coal- 

 basin, and have converted a part of the coal sandstones into red sand- 

 stone, which, as well as the porphyry, is entirely wanting in Upper 

 Silesia. Near the points of contact a portion of the coal is even 

 charred, and assuredly the high temperature, even though not above 

 that of boiling water, to which in consequence of this violent cata- 

 strophe the coal-beds were for a long time exposed, contributed much 

 to the more complete conversion of the vegetable matter into stone- 

 coal, whence we may easily explain the rare occurrence of vegetable 

 structure in this locahty. The remarkable activity of the waters at 

 that period is also proved by the innumerable conglomerates, of all 

 dimensions, found in the carboniferous sandstones, which seldom 

 show the almost uniform fine granular character of the same forma- 

 tion in Upper Silesia. [J. N.] 



On the Geographical Limits of the Chalk Formation. 

 By Leopold von Buch. 



[Monatsberichte der Akademie der Wissenschaften zu Berlin, fiir 1849, p. 117. 

 Compare also, Betrachtungen iiber die Verbreitung und die Grenzen der Kreide- 

 Bildungen ; Bonn 1849. Aus den Verhand. des naturhist. Ver. der Pr. Rhein- 

 lande.] 



The small extent towards the poles which the chalk formation at- 

 tains, compared with the Jurassic strata, and still more with the pa- 

 Iseozoic deposits, has been regarded by Dr. Boue, not without some 

 probability, as the most ancient known effect of the influence of 

 climate on the fauna of former worlds. In reality the most northerly 

 point on the whole earth in which chalk has as yet been found is, 

 according to Prof. Forchhammer's determination, in the vicinity of 

 Thistedt in Jutland, not quite in 5 7 degrees of latitude, or in that of 

 Aberdeen in Scotland, of Calmar, Mitau, Twer and Casan. In the 

 British islands the chalk does not reach so far north ; the last appears 

 on the south coast of the island of Rathlin near the Giant's Causeway, 

 in the latitude of Apenrade, of Bornholm and of Tilsit. Flamborough 

 Head in 54° is its last appearance in England. In Russia this limit 

 always sinks deeper towards the south. From Grodno, where the 

 chalk still appears in 54°, it runs, as laid down in Murchison's 

 masterly geological map, through Mohilew and Orel, a degree and 

 a half of latitude south of Moscow, and from Simbirsk downwards 

 along the Wolga, even to the Caucasus. MM. Murchison, Vemeuil 

 and Keyserling have very unexpectedly discovered this chalk on the 

 banks of the Ural river, ninety Enghsh miles below Orenburg, in 51 J°. 

 The Muchodjar mountain determines its hmits towards the east. The 

 immense extent of Siberia from the Ural to Ochotzk, and from the 

 Altai to the Icy Sea, has now been so minutely and carefully exa- 

 mined by so many mining engineers, naturalists and gold-seekers, 

 that we may well doubt of the occurrence of cretaceous beds in this 

 whole region. ... : 



Everywhere along this border only the \i^per chalk appears, the 



