398 NOTICES OF NEW BOOKS. 



1836, and referred by him to birds, he (the Professor) has observed 

 above 2000 footprints, probably made by nearly thirty distinct 

 species. (Vol. i. p. 254.) The beds of this age in Connecticut include 

 a fine-grained slaty sandstone, black and bituminous, and about six 

 feet thick, which alternates with a coarse conglomerate. Small 

 fragments of fossil wood and a ripple-marked surface were ob- 

 served in some of the strata near the fossil fish. The only other 

 rocks considered to belong to the older secondary period in North 

 America are the coal measures of Eastern Virginia referred by 

 Professor W. B. Rogers to the Oolitic period, but concerning 

 these Mr. Lyell does not offer an opinion. 



Our author's views of the cretaceous rocks of America will be 

 found fully expressed 'in the earlier pages of this volume (see 

 ante, p. 55.), and the tertiary strata will be described in similar 

 detail in the next number. 



In addition to those accounts of descriptive geology which come 

 properly under consideration in speaking of the succession of strata, 

 Mr. Lyell's work also contains some interesting facts and observa- 

 tions on the subject of [changes effected, in comparatively modern 

 geological epochs, by means of causes now in action. The geo- 

 graphical and geological features of the great Falls of Niagara 

 occupied, as might have been expected, a considerable portion of 

 his attention. With regard to the origin of these Falls, and the 

 rate of their recession, (for of the fact of their recession there is 

 distinct proof), we also have some speculations which cannot fail to 

 be viewed with considerable interest. The superficial covering of 

 gravel, the presence af erratic blocks, and the existence of horn- 

 blendic and syenitic rocks, polished, furrowed, and striated, as 

 seen in the north of Europe and in Switzerland, are also described 

 and referred to by the author, in the course of his various journeys 

 and traverses in various parts of North America. Numerous 

 localities, in addition to the well-known salt-lick of Kentucky, 

 are mentioned, in which the remains of that singular animal the 

 Mastodon have been met with, frequently indeed associated 

 with materials which prove how very recent must have been the 

 date of its existence, as a regular inhabitant of that part of the 

 world. It appears that in some places near Niagara the bones 

 are found associated with shells, all of existing species now com- 

 mon in the district, but buried in shell marl below the peat, 

 and therefore agreeing in position with the large fossil elks of 

 Ireland. 



The extensive swamps of North America afford matter of con- 

 sideration to the geologist, and Mr. Lyell gives (vol. i. p. 143.) 

 an account in some detail of one of the largest of them, known as 

 the Great Dismal Swamp. This singular expanse of soft and 

 muddy quagmire extends forty miles from north to south, and is 

 in some places twenty -five miles broad. It is at a higher level 

 than the surrounding dry land, and, even in spite of its semi-fluid 

 character, is about twelve feet higher in the middle than towards 

 the margin. The conditions of existence of this swamp and its 



