PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 505 



level, and tliat, tlierefdvo, instead of the eartli having snnk and carried the 

 trees down with it, the water must have risen upon the trees to that eleva- 

 tion, by the danuning of the old channel of Keel-fi^ot River. 



But how could the earthquake throw up this sand to the surface ? Hei*e 

 a little geology is demanded. In the future, I may describe the Artesian 

 wells of the countr}'^, a little south of the section under consideration. 

 These wells arc supplied with water, from a water-bearing bed of sand, 

 underlying, at a depth of several hundred fe(?t,' the chalk formation of that 

 region. This water-bearing sand-bed underlies the region disturbed by 

 the enrth(|uake; and is here overlaid by a bed of compact, tenacious clay, 

 in which the sides of o.rdinary wells, dug in it, will remain for years with- 

 out curbing. A fissure produced in this clay, would present smooth sides 

 to the bottom, and permit any fluid or gas to rush up to the surface, on the 

 application of force from beneath. 



A description of these two deposits will be more apprepriate, as I have 

 said, in connectwn with a notice of the Artesian wells further southward. 

 Here, in the area disturbed by the earthquake, it need only be remarked, 

 that we have a surface deposit of compact clay, of considerable thickness 

 underlaid by a deposit of sand, measuring a hundred feet in thickness, at 

 distant points where it crops out at the surface. Tliis bed of sand is com- 

 pletely saturated with water; so much so, indeed, that a well dug tlirough 

 the clay into it, at certain points, is inexhaustible, and cannot be dipped 

 dry — the sand being liable to flow, like any other quicksand. 



The maimer in which the sand-biows were produced, may now be under- 

 stood. The expulsion of water from the earth, is no unusual thing, during an 

 earthquake. When tlie undulations of the earthquake rent the clay bed, -in 

 the district under consideration, the tremendous upward pressure seems to 

 have been amply sufficient to force the water of the sand-bed, together with 

 much of the sand itself, to the surface, and thus, as the supply from below 

 was ample, the amount of sand in the mounds could have easily been borne 

 by the uprising water through the fissures. 



It is true that the sand-blows, as they now appear, are not always 

 accompanied by fissures, nor the fissures by sand-blows. But as the latter 

 do not exist, excepting in the vicinity of the former, which are known to be 

 the product of the earthquake', it is probable that both had their origin at 

 the same moment. A bed of gravel, in some localities, in the sand deposit, 

 may have prevented any sand from rising; or the fissure may not have 

 extended downward to the quicksand, so as to form an open seam ibr the 

 water to rise; or, in some cases, after the rush of \Vater and sand to the 

 surface, a fissure may have again closed up; and, thus, we find sand blows 

 without fissures, and fissures without sand-blows. 



A word as to the character of the fissures. In the vicinity of Reel-foot 

 Lake, twenty-five years ago, eye-witnesses say that some of the fissures, 

 now partially filled up, were as much as fifteen feet in width, and two 

 miles in length. In passing from Troy to Covington, Tennessee, in a 

 southern direction, I had ample means of examining the fissures upon the 

 route. They were first noticed a mile and a half north of Obion River, and 

 were from six inches to three or four feet in width, and from one to forty 

 rods long. On the southern side of Obion River, the sand-blows and 



