404 



SCIENCE 



[N. S. Vol. XXXIX. No. 1002 



The Development of Some Lake Beds in Florida: 



E, H. Sellakds. 



This paper relates to the origin of the basins of 

 the large flat-bottomed lakes found throughout 

 certain parts of interior Florida. These lakes are 

 often of considerable size, although relatively 

 shallow as compared to their areal extent. More- 

 over they are variable in character. Under nor- 

 mal conditions they are clear water lakes abound- 

 ing in fish and the favorite haunt of the wild duck. 

 They have, as a rule, no surface outlet, yet from 

 many of them the water has at times disappeared 

 in a manner seemingly inexplicable. Among the 

 largest and best known examples are: Lakes 

 Lamonia, Jackson and Lafayette in Leon county; 

 Miccosukie in Jefferson county; Alligator in Co- 

 lumbia county and Alachua in Alachua county. 



These lakes occupy basins which have worked 

 their way down through the surface sands and 

 clays probably of the Alum Bluff formation to or 

 nearly to the underlying limestones which are of 

 either the Chattahoochee or the Vicksburg forma- 

 tions. The beginning of each basin dates from 

 the formation of a sink making an opening 

 through to the underlying limestone, thus di- 

 verting the surface drainage to a subterranean 

 course. The small basin resulting from a single 

 sink is enlarged by the formation of additional 

 sinks, this process being promoted by the consid- 

 erable amount of the surface water that is ad- 

 mitted into the underlying limestone, particularly 

 when the sink has formed in the valley of an ex- 

 isting stream. The depth of the basin is limited 

 by the underground water level since the streams 

 can not well carry away the residual material be- 

 low this level. As a matter of fact the basins ap- 

 proach but do not quite reach the underground 

 water level. 



The ground water level is not stationary but is 

 subject to seasonal and periodic variations, as 

 well as to variation in geologic time. The sea- 

 sonal fluctuation is due to the variation in rain- 

 fall during the wet and dry seasons. The periodic 

 variation is due to the more or less regular peri- 

 ods, often of some years duration, of deficient or of 

 excessive rainfall. The gradual lowering of the 

 underground water level during geologic time, 

 which i3 due to the downward cutting of stream 

 channels which serve as an outlet, affects the life 

 history although not the observed behavior of the 

 lakes. The seemingly sudden emptying of the 

 lakes is in most cases due actually to the water 

 having gradually run out into the underlying lime- 

 stone because of the ground water level having 



been lowered by prolonged drought. New sinks 

 are likely also to form at this time since the low- 

 ering of the underground water withdraws the 

 support from the surface materials which are then 

 no longer able to support their own weight and 

 hence break through to cavities in the underlying 

 limestone. These new sinks when formed facili- 

 tate the emptying of the lakes. 

 A New Gypsum Deposit in Iowa: Geoege F. Kat. 

 In this paper some interesting facts are pre- 

 sented with reference to a gypsum deposit recently 

 discovered at Centerville in southern Iowa. The 

 gypsum is of Mississippian age and is associated 

 with anhydrite. Whether or not the gypsum will 

 prove to be of economic importance has yet to be 

 determined. The evidence indicates that the de- 

 posit may be extensive and the gypsum is of good 

 quality. The relation of the anhydrite to the 

 gypsum and the relative amounts of the two 

 minerals will have an important bearing upon the 

 value of the deposit for commercial purposes. The 

 fact that the deposit is more than 500 feet below 

 the surface and the presence of large amounts of 

 artesian waters are factors unfavorable to the min- 

 ing of the gypsum. On the other hand, the de- 

 posit is well located with regard to fuel and trans- 

 portation, and it is fair to assume that if gypsum 

 products were made in this part of the state a 

 good market for such products could soon be de- 

 veloped. 

 The Development of Some Underground Streams: 



Edgar H. Webster. 

 A Comparison of the Ordovician Section of South- 

 west Virginia, with that of New York: S. L. 

 Powell. 



In view of statements not infrequently made to 

 the effect that the Ordovician of Virginia and the 

 South in general can not be correlated with the 

 New York section, and in view of the fact that in 

 southwest Virginia, in the vicinity of Salem, 

 there occurs a continuous, unbroken section of 

 Ordovician strata about four thousand feet in 

 vertical thickness, very favorably disposed for ob- 

 servation, and as the locality is intermediate be- 

 tween the extremes heretofore most carefully 

 studied, detailed work was undertaken for pur- 

 poses of comparison with the standard sections 

 north. 



The results show that the correlation can be 

 made, and that in almost every detail, including 

 the divisions of the Beekmantown (Calciferous) 

 established by Brainerd and Seely of Vermont. 

 Without going into detail here, the main difference 



