174 Dr Martens on the Glaciers of Spitsbergen. 



from the neighbouring heights ; but the surface is never entire- 

 ly concealed under a layer of stones and sand, as takes place 

 with the lower glaciers. The reason of this may be easily un- 

 derstood. When a block falls on one of the upper glaciers, it 

 sinks in the snow ; as the latter never entirely melts, but is 

 converted into ice and is covered with successive layers of new 

 snow, it follows that the block is soon buried in ice. But the 

 glacier having a continued progressive movement, is always 

 descending towards the plain ; and while it advances over a 

 slope more or less inclined, the block advances horizontally, 

 and is soon placed at the surface of the glacier. Such, at least, 

 is the explanation given by M. Charpentier.* Hence the ex- 

 istence of the central moraines (Gufferlinien) which are the 

 union of the terminal moraines of several glaciers converging 

 into one, and which reject at their surface the blocks which 

 they transported enclosed in their substance. 



But it may be said that no one has ever seen in Switzerland 

 these blocks of stone immersed in the thickness of the superior 

 glaciers. This is true ; but it is forgotten that the upper gla- 

 ciers of Switzerland rest with both their sides on the moun- 

 tains, and do not therefore admit of their lateral parts being 

 examined throughout their whole height. Those of Spitzber- 

 gen, on the contrary, are disengaged from the surrounding 

 mountains and advance on the shore, so that their sides can 

 be studied as well as their surface. 



Some skilful observers, Hoffmannt among others, still main- 

 tain the opinion formerly advanced by Saussure. " As the 

 valleys," says this great observer,^ " have all more or less the 

 form of a cradle, and their bottoms more excavated than their 

 margins, the masses of ice become compressed and tend to- 

 wards the middle of the valleys : those which are at the sides 

 are removed from them, slip towards the lowest point, and 

 carry along with them towards the middle of the valleys the 

 earth and stones with which they are covered." 



Whether we adopt one or other of these theories regarding 

 the existence of blocks in the middle of glaciers, whether we 



* Gilbert's Annalen der Physik, t. xliii. p. 388. 1819. 

 t Physikalische Geogxaphie, t. i. p. 287. 

 I L. c. § 537. 



