330 MOUND EXPLORATIONS. 



thrown up by the waves oii the banks, and some of the shells, particu- 

 larly the more perfect ones, are so ronnd and light that they have sim- 

 ply been blown by the wind from the sides of the mound, scattered for 

 a mile or two over the surface near the sandy beach, but not carried 

 inland further than open spaces would permit a brisk breeze to blow. 



'• Deep treiiches have been dug in the orange grove to drain the 

 ground between the rows of trees. Into these trenches a certain nuni- 

 ber of the shells from the surface have been blown or have fallen. 

 Beside these, however, at a depth of 2 or 3 feet from the surface is a 

 layer of mud full of shells of all sorts, and which appears to be a west- 

 ward extension of the present swamp. This marl and mud appeared 

 to be abont 2 feet thick in most places and rested on a hard eolian 

 sandstone resembling the phosphatic rock of western Florida in appear- 

 ance, but much younger in age, full of recent land shells, and in which 

 Pourtales and Wyman both found human bones imbedded at Rock 

 island in Lake Monroe. 



"Behind the sand of the beach a little lagoon was originally formed, 

 in which gradnally accumulated the mud from decaying vegetation 

 brought down by the streams or growing on the spot. Here tlonrished 

 the Unios, Yinpantx, etc., and in time formed a bed of mud and marl. 

 Upon this the wind blew sand from the, beach, and in this way the dry 

 land has grown. The marl in position is rather soft, but when well 

 drained it becomes very hard, almost forming a stone. The shells in 

 it are just as they died, large and small, mostly in good condition, 

 except the Unios, which are more perishable than the univalves, and 

 always less perfect. The Yiviparas are thin and light, but very strong, 

 and a layer of them will sustain a weight of 150 pounds without break- 

 ing. Owing to the air they contain they are very buoyant, and a com- 

 pact layer 4 inches thick spread over the soft mud of the swamp will 

 sustain the weight of a man, a fact which I personally tested. Besides 

 the whole shells, there is a large amount of broken and decayed shelly 

 matter. The large AmpullariaH are very fragile and may have been 

 broken up, but at all events are very rare in the marl. I saw no per- 

 fect ones. 



"The shore and bottom of the lake near the mound, and as far as 

 could be observed into the deep water, are composed of clear sharp 

 sand, affording no food or resting place for mollusks, and neither dead 

 nor living ones are found in it, except su(^h as may have been washed 

 from the mound. The mound itself probably stands partly on the 

 original sea beach and partly on the swamp. 



" The way in which its materials have been scattered about prevented 

 the attainment of certainty in the matter, but the above suggestion 

 accords with what was observed. About two-thirds of the mound has 

 been dug away nearly to the level of the beach. In 1848 the bluff, 

 where the storms had washed away the lakeward slope, was 15 feet 

 high. The summit of the mound was about 5 feet higher, and on it an 



