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MODEL OF VESUVIUS. 



161 



cliffs, this sandstone, when it stood at a different level, was 

 formed into cliffs by the same kind of marine denudation 

 that now forms the cliffs of the chalk. 



Nos. 4 & 5 are models of parts of a country formed of 

 gneiss. In No. 5 the numerous vertical and highly-inclined 

 joints are remarkable, especially the curved form they 

 assume on the side next the printed title. (Gneiss rocks at 

 the entrance of the Bay of Morlaix.) The great irregularity 

 of the coast line is evidently partly due to the multitude of 

 joints, parts of the rocks having offered less resistance than 

 others to the denuding force of the waves. 



Nos. 6 & 7 are models of inclined limestone rocks in the 

 neighbourhood of Sable (Sarthe). — A. C. Ramsay. 



Upper 

 Gaxleey. 



Wall-case 3. 



Table Case in Recess $. 



Topographical and Geological Model of Vesuvius and Spe- 

 cimens illustrative of Vesuvius and its Neighbourhood. 



In the model, constructed by M. Dufrenoy in 1838, the 

 horizontal and vertical scales correspond. The order cf 

 age, or superposition, of the different rocky masses, seems 

 to be as follows, beginning with the oldest. 



Trachyte spreading from Portici to Pompeii on the 

 coast and up to the base of Somma. 



2nd— Leucitic lavas of Somma. Many of the specimens 

 frorn No. 66 onward are derived from these, and where the ; 

 locality is certain they are marked " Somma." 



" ' Pumiceous tufa or ashes, &c, spreading from 

 Naples to Portici and round the further side of the moun- 

 tain to Pompeii. These are chiefly marine and contain sea 



1st. 



3rd. 



shell 





s. These rocks are intimately connected with No. 2 

 4th.— Tufa of Pompeii. 



5th.-Modern lavas, &c, Nos. 1 to 65, erupted since 



Aj). 79.— A. C. Ramsay. 



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