94 ALLUVIUM, OR MODERN DRIFT. 



and sixty feet in length, by twenty feet broad, and forty feet high, 

 while between the Jura and the Alps blocks still larger are in 

 many places to be found one, out of a great number together in 

 the canton of Berne, measuring 01,000 cubic feet. 



37. Erratic blocks and gravel cover the plain of central Europe 

 and the steppes of Russia. Almost the whole surface of North 

 America, as far as it has been examined, has been found covered 

 with gravel, pebbles, and boulders, varying greatly in thickness, 

 and obviously of the same origin as similar deposits in Europe ; 

 and a region which has been called the great Atlantic plain, ex- 

 tending between the Alleghany mountains and the Atlantic ocean, 

 together with the lower part of the great valley of the Missisippi, 

 appear to* be the districts where it conceals the underlying deposits 

 to the greatest depth. 



On the borders of Lakes Erie and Ontario there are very de- 

 cided marks of the great drift which has elsewhere overspread 

 North America, and the boulder formation, containing marine 

 shells, extends into the valley of the St. Lawrence, as far down as 

 Quebec, and at a height of at least three hundred feet above the 

 sea-level. Below duebec there are large and far-transported boul- 

 ders in beds, both above and below these marine shells, and 

 wherever the contact of the drift with hard subjacent rocks is seen, 

 these rocks are smoothed and furrowed on the surface, as they are 

 in similar positions in northern Europe. 



38. ALLU'VIUM, or MODERN DRIFT. In many parts of North 

 America the valleys are filled up to a depth of twenty or thirty 

 feet with unconsolidated beds of earth of various kinds, and the 

 heteroge'neous mass contains in it abundant remains of large 

 pachydermatous animals, not now living in the country, but asso- 

 ciated with, and overlaid by other and similar beds, in which occui 

 the bones of buffaloes, that have within a few years been driven 

 westward by the advancing steps of civilized man. These beds 

 all belong to the same geological period, or nearly so, and a descrip- 

 tion of one will be sufficient to give an accurate notion of a multi- 

 tude of similar bogs and soft meadows in many of the western 

 states. The most remarkable is that known as the " Big Bone 

 Lick" in Kentucky. 



39. The Big Bone Lick occupies the bottom of a boggy valley, 

 kept wet by a number of salt springs, which rise over a surface of 

 several acres, and the substratum of the country is a fossil i'feroua 

 limestone. At the Lick the valley is filled up to the depth of not 

 less than thirty feet with beds of earth, the uppermost of which is 

 a yellow clay, apparently the soil brought down from the high 

 grounds by rains and land floods. In this yellow earth, along the 



37. Where is the Boulder formation met with ? 



38. What is allu'vium ? 



39. What are the characters of the Big- Bone Lick of Kentucky ? 



