Frazer.] ^oS [April 21, 



NOTE ON THE "LITIIOLOGIE DU FOND DES MEllS " OF 



M. DELESSE. 



By Pkof. Persifou Fkazeu, Jr. 



(Bead before the American Philosophical Society, April 2\8t, 1876.) 



M. Del('«se acknowledges his indebtedness to tlie treatises in Geology 



of Eiie de Heiiuniont and Jus. D. Dana, in the first few prefatory pages. 



The following shows the scope and direction of the work: 



I. Preliminaries. Methods pursued in studying the deposits. Oro- 

 graphy of France and her sultniarine shores. 



II. Principal agents of marine deposits. 



Organic agents. 



r A.tmosphere. 

 'External s Fresh and brackish waters. 

 (The Sea. 



Inorganic agents 



Subterranean waters. 



Internal < Erupticms. 



' Dislocations. 



III. Marine deposits of the Coast of France. Shore deposits and sub- 

 marine deposits. Distribution of Mollusks. 



IV. Lithology of the principal seas of the globe. France, The ancient 

 world. The modern Avorld. 



V. France at difieient geological epochs. Deposits of the ancient seas 

 of France. Changes undergone by these deposits. 



M. Delesse then describes his methods of investigation. 



Fine sand is treated with hydrochloric acid, its loss of CO^ determined, 

 and this multiplied by 2.27 to obtain the carbonate of lime. This method 

 is accurate enough. Magnetic iron is separated by a magnet. Part of the 

 gangue comes out with the magnet. This augments the magnetic sand on 

 the one liand ; on the other much of the magnetic Siind is not taken up ; 

 so that tliese two errors are on opposite sides. 



Sands and gravels examined contained 0.54 to 2.70 p. c. of soluble 

 material (sea salts and organic matter). Argillaceous sand has a tendency 

 to remove salts from the water containing them. 



The classification of the deposit was had without recourse to chemical 

 analysis, by the microscope. 



The sieve used had meshes with a diagonal of 1 mm. TIic universality 

 of the presence pf quartz is very striking. Even vegetable mould and that 

 too resting on calcareous rocks show a notable proportion of quartz. 

 Quartz is more abundant the more the waters are agitated. 



Tiic sand dunes of the coasts of France arc mainly composed of hyaline 

 qiiartz, whitish gray. They slope gently towards the sea at about 7°; land- 

 wards about 29'^ to 35^^, and have been seen to advance in a high wind in 

 spite of a heavy fall of rain 0.6 m in three liours. The absence of mud in 

 dunes is noteworthy but easily explained, since this substance landers the 

 formation of dunes. 



The minimum rainfall in France is in the region bordered by Troyes, 

 Meaux, Compiegne, Epernay (40 centimetres). 



