38 



Da Farven er et karakteristisk Kjendemærke for den 

 ydre Adskillelse af de forskjellige Sedimenter, maa det være 

 af Interesse at kjende deres dermed sammenhængende kemi- 

 ske Egenskaber. I denne Anledning maa vi rette vor Op- 

 mærksomhed mod den Oxydationsgrad, hvori Lerets Jern- 

 mængder befmder sig. 



For at faa saa mange Observationer som muligt i 

 denne Retning bar jeg samtidig med Kalkbestemmelserne 

 tilberedt mig et saltsurt Udtræk (paa den forud omtalte 

 Måade) af den samme Prøve, hvis Kulsyregekalt var fundet 

 ved Johnsons Apparat. Jernoxydul er titreret med Kamæ- 

 leon og Jernoxyd med undersvovlsyrligt Natron og Jod- 

 oplosning 1 . 



Som de senere Analyser vil vise. indeholder det 

 saltsure Udtræk den væsentligste Del af Lerets samlede 

 Jernmængde. 



Graat Ler. 



Undersøgelsen af de talrige Bundprover (over 150), 

 der er indsamlede paa Kystbankerne rundt det europæiske 

 Nordhav, har godtgjort, at den graa (stundom blaagraa) 

 Farve i Almindelighed er en iælles Egenskab for alle de- 

 Slamdannelser. der bedækker disse grundere Dele af Hav- 

 bunden. I andre Retninger er imidlertid dette graa Ler 

 af en temmelig uligeartet Beskaffenhed. 



Paa nogle Stationer tinder vi det som en tin plastisk 

 Masse, der ved Tørring trækker sig stærkt sammen og 

 danner en haard Klump af en saadan Fasthed. at man 

 ofte maa bruge en Hammer for at slaa den istykker. 

 Andetsteds er Leret mere porøst og grovkornigt; det kryber 

 kun lidet sammen ved Tørring og bliver blot løst sammen- 

 hængende. 



1 )enne riigeartethed er afkængig af Biblandingen af 

 grovere Materiale i Form af Sand (Kvartskorn) og uorga- 

 niske Dyrelevninger. 



Naår vi underkaster Leret en Slemning for at under- 

 søge dets Blandingsforhold, faa.r vi et større eller mindre 

 Residuum. der hovedsagelig indeholder Skaller eller Skal- 

 brudstykker af kalkafsondrende Dyr og grovere mineralske 

 Partikler. I )e sidste bestaar som oftest for en væsentlig 

 Del af smaa Kvartskorn. der i Almindelighed er noget af- 

 rundede i Kanterne. I hvilken hoi Grad dette uforgjænge- 

 lige Mineral er fremherskende fremfor de øvrige i Afleirin- 

 gerne paa de grundere Dele af Havbunden, er paavist af 



Delesse i lians \":erk : "Lithologie dll fond des mers" 



En påalidelig kvantitath Slemningsanalyse lader sig 

 vanskelig udføre i de tørrede Bundprøver. Ved Kogning 

 mud Vand kan man vistnok faa den faste Lermasse opblødtj 



Colour being the chief external feature distinguishing 

 oceanic deposits, it must obviously be of interest to learn 

 wkence that character is derived; and on investigating the 

 subject, we tind chemical agency to constitute the origina- 

 ting cause, - - viz. the more or less advanced stage of oxi- 

 dation in which the iron of the deposit occurs. 



With a view to elucidate this question as fully as 

 possible, I prepared. when performing the carbonate of 

 lime determinations, a separate hydrochloric acid decoction 

 (in the manner previously described) of the same sample of 

 deposit in which the proportion of carbonic acid kad been 

 found with Johnson's apparatus. The protoxide of iron in 

 this decoction was titrated with permanganate of potash 

 and the sesquioxide with hyposulfite of soda and solution 

 of iodine. 1 



From the subsequent analyses it will appear that the 

 hydrochloric acid decoction contains the greater part of 

 iron present in the deposit. 



Grey Clays. 



A comparative examination of the numerous samples 

 of the bottom (upwards of 150) collected on the coastal 

 banks of the North-Atlantic, has shown that, as a rule, the 

 grey or bluish-grey colour constitutes a distinctive feature 

 common to all sedimentary deposits covering the shallower 

 portions of the sea-bed. In other respects, bowever. this 

 clay differs very considerably. 



At some of the observing-stations it was found to 

 occur as a fine, plastic substance, which. when dried. con- 

 tracts into a lunipy mass, so hard and compact that a hammer 

 has frequently to be used for breaking it. In other local- 

 ities. this coastal clay is more porous in character and 

 coarsely grånulated; it shrinks very little on exposure to 

 heat, aud has, when dry. but trifling cohesive power. 



This warit of homogeneity arises from the presence 

 of coarser materials, such as sand (quartz) and inorganic 

 animal remains. 



On tboroughly washing the clay. to determine the extent 

 of admixture, there will be found a greater or less residue. 

 composed chiefly of calcareous shells or fragments of such and 

 other mineral particles. Grams of quartz, as a rule rounded 

 at the edges, generally constitute the greater part of the 

 latter. The extent to which quartz predominates over other 

 mineral substances as a constituent of oceanic deposit in 

 the shallower parts of the sea-bed. has been shown by De- 

 lesse in his work -Lithologie du fond des mers." 



To obtain a trustworthy determination of the various me- 

 chanical constituents in the clay by washing. is hardlv practi- 

 cable. The concrete substance of the deposit may. indeed, 



1 Den sidsté Methode Kun vistnok ikke gjøre Fordring paa nogen 

 sim- Søiagtighed, men maa dog ansees for tilfredsstillende ved det 

 Imi i iggende i (iemed. 



1 Titration by this method does not indeed give ;i 1 1 i l: 1 1 degree 

 of accuracy,, but raaj for this purpose be regarded as yielding fairly 



satisfaetor\ rcsults. 



