172 Mr. De la Beche on the Geology of the 



copper nail in the limestone ;— and that of Mr. Allan in the Transactions of 

 the Royal Society of Edinburgh*, to which is added a list of the fossil and 

 sub-fossil shells by Captain Brown. 



Brhche en place. 



The most recent deposits of this country present several peculiarities which 

 claim attention. They assume in general the form of a breccia; but of this 

 breccia there are two kinds, the one consisting- of deposits on the surface, the 

 other lodged in fissures and caverns : — they appear to be very much con- 

 nected. 



The fragments included in the surface breccias agree for the most part 

 with the substance of the rocks immediately beneath ; a few only are rounded, 

 and appear to have been brought from a distance. Their cement is mostly 

 calcareous, and varies in hardness and colour with the nature of the sub- 

 stratum ; when it rests on dolomite or light-coloured compact limestone, it is 

 often so hard as to require blasting : it is sometimes reddish and vesicular, the 

 vesicles being lined with minute crystals of carbonate of lime : where it rests 

 on marly or sandy limestones, or on tertiary beds, it is soft, friable, and for 

 the greater part white. 



Most of the breccias in place are derived from the rocks in their immediate 

 vicinity ; thus resembling many of those deposits in England and France 

 which clearly show a destruction of the rocks almost in place, as may be well 

 seen in the accumulation of chalk flints and chert upon the hills near Lyme 

 Regis and Sidmouth, and is particularly well exhibited in Normandy. 



Sub fossil Shells. 



Between Villefranche and St. Hospice, the breccia reposes on a loose light- 

 coloured sand, full of shells, which so nearly resemble those of the Mediter- 

 ranean, that they have been called sub-fossil : though generally bleached, 

 there are some which retain traces of their native colours. — Lists of these 

 shells are published in M. Risso's work, and in the Transactions of the Royal 

 Society of Edinburghf . 



In Villefranche Bay and Beaulieu, this shell bed is covered with whitish 

 marl, including fragments of calcareous grit : the marl occurs over the whole 

 tongue of land; and the shell bed is probably beneath il, though not every 

 where visible. 



The shell bed in Villefranche Bay is from ten to twenty feet above the 

 Mediterranean, shelvin": to the sea level at Beaulieu. 



* Vol. viii, p. 427. f Vol. viii. p. 459. 



