76 Mr. Lyell on a recent Formation of 



Near the old castle, marl of pure quality has been sunk through of the re- 

 markable thickness of more than 16 feet. In the Loch of Restennet it is 

 said to be equally thick. 



The tufaceous limestone or rock-marl is limited to the vicinity of the springs, 

 which occur distributed irregularly over the lake. A small part of it only can 

 ever be examined ; since those spots where it is abundant, from its impeding 

 the casting of the shell-marl, are avoided. It belongs to the upper or great 

 bed, if exclusively belonging to either of the two beds of marl ; but this point 

 is uncertain, since in the two following sections, which are the only ones that 

 I succeeded in obtaining, the sand No. 3, which usually divides the upper 

 bed of marl from the lower, is wanting. 



Section immediately/ to the South of the great Spring. 



Thickness. 

 Ft. In. 

 1. Tufaceous limestone or rock-marl, forming a solid continuous stratum, extending ■» 

 on the surface over many square yards J 



I 2 4 



2. Soft marl, containing throughout its whole substance many flattened concretionary -j 



masses of tufaceous limestone or rock-marl 



3. Sand, without pebbles, bored to the depfh of 2 2 



Section on the side of the great Drain near the great Spring. 



Thickness. 

 Ft. In. 

 J. Soft-marl 10 



2. Ditto, sometimes sandy with concretions of tufaceous limestone or rock marl ... I 6 



3. Loose sand unknown. 



The shell-marl of the Bakie is white, with a very slight tinge of yellow, 

 and is less mixed with vegetable matter than the marl of other neighbouring 

 lakes ; a consequence, probably, of there not being any stream, however 

 small, which enters the lake, and by which foreign matters can be drifted into 

 it*. It rarely consists of distinguishable shelly matter in large proportion; 

 and in some parts of the lake, paiiicularly in the vicinity of the springs, is a 

 pure calcareous substance, free from every trace of organization. This latter 

 variety of marl is unctuous when in a moist state; and when dried, it much re- 

 sembles the softest varieties of chalk, though somewhat more loose and pulve- 

 rulent. 



The limestone or rock-marl has the same yellowish tint as the shell-marl. 



* When a stream enters a lake, peat is drifted in, and deposited at the bottom. Thus in the 

 Loch of Forfar, from which shell-marl is annually dredged, the surface is found covered with a 

 thin fluid peat, which it is necessary to begin by removing. 



