752 APPENDIX. 



Missouri River, and exists in small quantities as far south as the Osage and 

 Meramec : the thickness is from one to forty-five feet; the greatest thickness 

 and coarsest material are to the north. The boulders or rounded stones consist 

 of metamorphic rocks and fossiliferous limestone ; the nearest locality of the 

 former in place, according to Owen, is on the St. Peter's River, about 300 miles 

 north of St. Joseph ; the latter are from localities near where they occur, as is 

 shown by the fossils. The largest boulders are five to six feet in diameter. The 

 Drift is underlaid in several counties (and perhaps generally) by a layer of pipe- 

 clay, one to six feet thick (Swallow). 



There is no Drift in Arkansas, except that of a local origin (D. D. Owen). 



With regard to oblique scratches up and down declivities, Professor Guyot 

 states, in a letter to the author, that they are a common result of glacier-action 

 in Switzerland. The most of the scratches on the Jura Mountains are of this 

 description. As the great glacier of the Rhone moved against their sides and 

 became deflected thereby, there was, as a resultant (on the northeast side at 

 least), a running up obliquely of the whole mass at the same time that it moved 

 eastward and down the general slope of the country. 



To appreciate the effects of a vast glacier over a continent or occupying the 

 whole breadth of a wide valley, — like that of the Hudson between the summit 

 of the Green Mountains on one side and that of the Catskills on the other, — it 

 must be remembered that a general southerly movement in the whole mass 

 would carry the boulders and scratch surfaces, transversely or obliquely, across 

 subordinate transverse valleys and ridges, ascending or descending declivities. 



It is to be noted, in connection with this subject, that powerful torrents flow 

 for some distance beneath all glaciers, and from their terminations; and the 

 effects of such torrents are naturally mingled with true glacial effects. 



Agassiz and Guyot, of Switzerland, who are familiar with both the Swiss and 

 American facts, adopt the Glacier theory of the drift. 



E.— Coral Reefs (pp. 587, 591). 



1. Rate of growth of corals. — The author is indebted to Captain E. B. Hunt, 

 U.S. Engineers, for the following definite facts with regard to the rate of growth 

 of species at Key West, southwest of the southern cape of Florida. 



Over a bottom in ten feet water which had been cleared in 1846, a Meandrina 

 grew in the course of eleven years to a hemisphere (the usual form of the spe- 

 cies) six inches in radius. 



This is equivalent to six-elevenths of an inch a year ; and, allowing one-third 

 for the porosity of the coral, it corresponds to an upward increase in solid bulk 

 of four -elevenths of an inch, — which is almost identical with the three-eighths 

 deduced on page 591. 



An Oculina — a branching coral growing in clumps — grew at the same place, in 

 twelve years, to a height of nine inches and a breadth of twelve inches, equiva- 

 lent to three-fourths of an inch a year. This coral has few pores ; but the 

 branches are small, being hardly a fourth of an inch thick at the extremity, and 

 the spaces between them are from one to one and a half inches. The amount 

 of increase is not equal to that of the Meandrina. 



2. Florida reefs. — The rock of the reef at Key West is mainly an oolitic lime- 



