168 W. H. Dall— Geology of Florida, 



probably followed it at no very great interval, geologically 

 speaking. 



The Caloosahatchie River, in the proper sense of the word, 

 begins at the northeastern extreme of the long estuary which 

 bears the name, some distance above the town of Myers. 



The banks at first are extremely low and screened by thickets 

 of mangroves which only disappear when the water becomes 

 perfectly fresh. The land appears nearly level. As the river 

 is ascended a close scrutiny shows that it cuts through a suc- 

 cession of gentle waves gradually increasing in height inland, 

 whose crests would show a general parallelism with the direc- 

 tion of the peninsula of Florida, or transverse to the average 

 course of the river. Near the head waters of the river these 

 waves of elevation rise above the level of the river at low water, 

 to a height of perhaps twelve feet at most, and their individual 

 length from one trough to another may average about a quarter 

 of a mile. Though insignificant as flexures they are interest- 

 ing as showing that a lateral as well as a vertical thrust has 

 attended the movements of the rocks in this part of the State, 

 a fact which has been questioned. 



The greatest elevation studied by us extends for several 

 miles between the sites of the old forts Thompson and Deneaud. 

 At the former point the canal from.Lake Okeechobee enters the 

 river, its bed being a compact rock which had to be blasted 

 out. The succession of the strata is perfectly uniform, though 

 the amount of their fossiliferous contents varies. 



A section of the south bank, about two miles and a half 

 below the end of the canal, gave eighteen inches humus and 

 sand over the same depth of indurated yellow sand without 

 fossils, below which are two feet of sandy marl with Bulla 

 striata, Venus cancellaia, and a multitude of Planorbis and 

 Physa ; then three feet of compacter marl with a great many 

 marine fossils and comparatively few fresh-water shells, the 

 deposit containing irregular nodules, lumps and strings of 

 silicified material often extremely hard, and in which the fos- 

 sils are often represented by mere molds. Below this, which 

 is the chief fossiliferous stratum, lies a foot and a, half of sand 

 and marl with few fossils but many fragments, and worn 

 siliceous fragments against which the water washes. This 

 stratum in other places is consolidated to a tolerably compact 

 rock, and the fossil bed abttive it to a flinty chert. The chert 

 shows manifest indications o\f having been worn by the action 

 of waves, and one of my specimens shows a boring bivalve 

 still intact in its burrow in one of the protuberances of this 

 layer. In other places fossil oyster-banks could be clearly seen, 

 but nowhere any coral reefs, though isolated heads of coral were 



