Scientific Intelligence — Geology. 9i% 



tal beds, through which the stems of the palms will be found to pass. 

 — {Travels in the Interior of Brazil, hy George Gardner, p. 110.) 

 16. Eruption of Mount Hecla. — The Royal Academy of Sciences 

 at Gbttingen petitioned the King of Hanover to send commissioners 

 into Iceland, at the government expense, for the purpose of observing 

 this phenomenon ; and two distinguished geologists, Messrs Berez 

 and Sartorius, were nominated for that duty. 



16. Observations on the petrifaction of Shells in the Meditev 

 ranean. By MM. Marcel de Serres and L. Figuier. — The object 

 of the authors of this memoir is to prove that phenomena are now 

 taking place in our own seas, altogether similar to those which have 

 produced the petrifaction of shells. They shew that, in the double 

 relation of chemical composition and mode of petrifaction, the shells 

 preserved in the bottom of the sea, are in every respect like those 

 which belong to the tertiary formations. The difference which exists, 

 between the mode of substitution at present times, and that of geo- 

 logical times, consists in this, that the petrifaction found in the his- 

 torical epoch, usually present a more crystalline texture. They do 

 not, however, become very compact, till they have passed through 

 different degrees. The investigations of MM. Marcel de Serres and 

 Figuier have related chiefly to oysters, pectens, venus, petunculi, and 

 cardium, genera found, at the same time, preserved in tertiary for- 

 mations, and in recent banks of rivers. {Supplement a la Bihlioth. 

 Univ. de Geneve, No. 8, p. 421. 



17. On Slaty Cleavage. — One law respecting slaty cleavage was 

 announced in 1831, by Professor Sedgwick,* and is now well known : 

 that law is, that the cleavage planes maintain their parallelism over 

 extensive areas irrespective of the varying position of the beds which 

 they cut through, or of the mineral character of the beds. Another 

 law respecting slaty cleavage was detected by the authorf in the 

 progress of his tour, and is the following : viz. that the strike of the 

 cleavage coincides with the strike of the bedding, whenever the latter 

 continues uninterruptedly the same for a considerable distance ; but 

 when the strike of the bed is inconstant, and shifts at short intervals, 

 then the cleavage planes hold their course right on, irrespective of the 

 varying position of the planes of bedding ; in other words, that the 

 strike of the cleavage coincides with the prevailing strike of the 

 beds in each district, and does not vary with the subordinate and 

 local irregularities in the strike of the beds. Whence it follows, that 



* Geol. Trans., 2d series, vol. iii., p. 68. 



t While the author was drawing this conclusion from his observations in 

 Wales a nearly similar law was announced to the British Association at Cork, 

 by Professor Phillips, in the following terms :— " The cleavage planes of the slate 

 rocks of North Wales are always parallel to the main direction of the great 

 anticlinal axis, but are not affected by the small undulations or contortions of 

 these lines. In North Wales they maintain the same direction for 50 miles, 

 not varying more than 2 or 3 degrees." (See Athenaeum, 2d September 1843.) 



