86 Mr. Lyell on a recent Formation of 



not my intention to dwell. It is well known that ancient freshwater deposits 

 in many cases consist almost wholly of loose materials^ such as marl, clay, and 

 sand, either disposed in alternating layers, or variously blended with one an- 

 other; and such also are the principal contents of the Bakie, and the entire con- 

 tents of most of the marl-lochs in Forfarshire. Between the aquatic plants and 

 animals of the two epochs the closest relation subsists, the genera in the two 

 cases being nearly identical. Thus we find in both formations: among the Tes- 

 tacea, — LymneaB, Planorbes, &c. ; among the Crustacea, — the genus Cypris ; 

 and among the plants, — the genus Chara, with its fossilized seed-vessel the Gy- 

 rogonite. Even between the terrestrial animals of the two epochs the relation 

 does not wholly fail ; since in both instances, imbedded in the deposits, occur 

 the remains of large Mammalia. Nor is the magnitude of the ancient fresh- 

 water lakes without a parallel among recent formations, although the modern 

 process of deposition may in most instances, either from a reduced scale of tem- 

 perature or from the smaller dimensions of the present race of testacea, be 

 comparatively slow. Thus the surface of Lake Superior alone is half as large 

 again as the area of the three tertiary basins of Paris, London and Hampshire 

 united, of which basins only very limited portions are occupied by freshwater 

 deposits ; and the same lake is considerably greater than the great tertiary 

 basin of the south of France. That these American lakes are forming depo- 

 sits, and the nature of the deposits so formed, we fortunately are enabled to 

 ascertain, in consequence of the subsidence of the waters of Lakes Superior 

 and Huron, occasioned by the partial destruction of their barriers. These de- 

 posits may be traced along their present shores: on Lake Superior they consist 

 of clay, sand and gravel; and on Lake Huron, below beds of sand 150 feet 

 thick, we have similar beds of clay, inclosing shells of the very species which 

 inhabit the lake, and which are of great size and thickness. [Dr. Bigsby in 

 the Journ. of Science, &c. No. ^7. pp. 262, 263.] 



On several other Recent Deposits of Freshwater Marl. 



Having now terminated my description of the freshwater deposits of the 



Bakie, I shall give a brief account of some other deposits of marl with which 



I am acquainted. 



L Marl of the Loch of Kinnordi/ . 



The Loch of Kinnordy lies in the same geological district with the Bakie, 



about 6 miles to the north-west of it*. It is closed up at its bar by a mass in 



* The loch, or rather the marl-meadows, of Logie are situate nearly in the same direction, and 

 at the same distance from the Bakie. 



