4 SMITHSOXIAX MISCELLANEOUS COLLECTIONS VOL. 52 



Equivalent to — 



Carbonate of lime ( CaCOs j 93-26 



Carbonate of magnesia ( MgCOs) 1 . 16 



Analysis of part of a concretion containing a so])icii'liat telescoped fossil fish 



{Rhacolepis buccalis) 



(Record Book ;Si) 



Silica (SiOs) 4-3i 



Iron and alumina ( Fe-Os and AI2O5) 3.05 



Lime (CaO) 50.39 



Magnesia ( MgO) 0. 66 



Loss (CO2 and water) 41-53 



Total 99-94 



Equivalent to — 



Carbonate of lime (CaCOs) 89.98 



Carbonate of magnesia ( MgCOs) i . 38 



Analysis of part of a concretion containing a fossil fish, Calainoplcuriis vestitus, 



Specimen N'o. 13 



(Record Book 782) 



Carbonate of lime (CaCOs) 90.64 



Carbonate of magnesia (MgCO^) i . 27 



Analysis of part of the concretion containing the large speciuicn of Calamo- 

 plcurus cylindricus received from Dr. Paula Pessoa, of Rio de Janeiro 



(Record Book 783) 



Carbonate of lime ( CaCOs) 92 . 57 



Carbonate of magnesia (MgCOa) i .25 



Many of the specimens of fossil fishes have been crushed together 

 lengthwise or telescoped, so that the scales are thrust farther over 

 than they should be. This peculiarity of these fishes has been noted 

 before by Dr. A. Smith Woodward in his paper published in the 

 Proceedings of the Zoological Society of London, 1887. The chem- 

 ical analyses suggest that this telescoping may be due to the partial 

 dolomitization and consequent shrinking of the original limestone 

 caused by the substitution of magnesium carbonate for the calcium 

 carbonate. 



The appearance of the rock and the analyses given above lead one 

 to suppose that the composition of the concretions is fairly uniform. 

 Some of them, however, are much more sandy than others, and the 

 specimens in the sandy rocks are not so well perserved as those in 



