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POPULAR SCIENCE REVIEW. 
falls have been known to Europeans about 200 years. The country is 
covered with deposits of glacial origin, and between Fort Snelling and 
the present Falls, a distance of eight miles, the existing river-gorge has 
been formed since the deposition of the newer Boulder-clay. The old 
river-valley is filled up with glacial deposits. The gorge is of very uniform 
character, being cut through hard limestones resting on soft sand rock, both 
lying quite horizontally. The country was settled in 1856, and the recession 
of the falls has since been vervj, rapid, its rate having been accelerated by 
the erection of saw-mills, dams, &c. From the accounts of various travellers 
who have visited the falls in the last 200 years, Mr. Winchell endeavours 
to obtain an estimate of the true rate of recession. Between the visit of 
Father Hennepin in 1688 and that of Carver in 1766 he finds a recession 
at the rate of 3*49 feet annually ; between Carver’s visit and 1856, a mean 
annual recession of 6*73 feet; and between Hennepin and 1856, one of 5T5 
feet. The time-estimates for the cutting of the gorge would be, according 
to the above means, 12, 103, 6, 276 and 8, 202 years. Mr. Winchell con- 
siders the data upon which the second of these numbers is founded the most 
reliable. Sir Charles Lyell’s estimate of the recession of the Falls of 
Niagara from the escarpment at Queenstown to their present site is 35,000 
years. 
The Mosasaurs. — Professor O. C. Marsh has obtained the materials for a 
complete reconstruction of the fore-limb of Lestosawus, an American type of 
Mosasaurs. Professor Owen has instituted a comparison of the characters 
of this limb, as shown in Professor Marsh’s figure, with the bones of the same 
parts in cetaceans, plesiosaurs, and lizards. He finds the characters pre- 
sented to approach most closely to those of the last-named order of Reptiles, 
of which Monitor niloticus was taken for comparison. Hence he regarded 
his view, originally stated in 1851, that the Mosasaurs form a tribe, Natantia , 
in the Reptilian order Lacertilia, as confirmed; and he compared the relations 
of these reptiles to the other lizards with those of the seals to the ordinary 
carnivorous mammals. — ( Proc . Geol. Soc ., 5 June 1878). 
PalcBozoic Rocks under London. — Professor Prestwich has given a most 
interesting account of the results of the deep well-boring recently made at 
Messrs. Meux’s brewery, at the south end of Tottenham Court Road. He 
remarks that the well-known boring at Kentish Town, in 1856, showed the 
absence at that point of Lower Greensand, the Gault being immediately 
succeeded by hard red and variegated sandstones and clays, the age of which 
was at first doubtful, but which were finally considered to approach most 
nearly to the Old Red Sandstone near Frome, and to the Devonian sand- 
stones and marls near Mons, in Belgium. The existence of some doubt as to 
:his identification rendered the boring lately made at Messrs. Meux’s brewery 
Darticularly interesting, and the method of working adopted by the Diamond- 
noring Company, by bringing up sharply cut cores from known depths, gave 
special certainty to the results obtained. The boring passed through 652£ 
feet of Chalk, 28 feet of Upper Greensand, and 160 feet of Gault, at the 
base of which was a seam, three or four feet thick, of phosphatic nodules 
and quartzite pebbles. Beneath this was a sandy calcareous stratum of a 
light ash-colour, passing into a pale or white limestone, and this into a rock 
of oolitic aspect. Casts and impressions of shells found in this bed showed 
