March 30, 1906.] 



SCIENCE. 



489 



of the trunks of trees have been observed 

 one half silieified, the other half lignitized. 



TOPOGRAPHY. 



The topographical features of the coun- 

 try covered by the Grand Gulf strata are 

 quite characteristic. Near the northern 

 border where the Vicksburg limestone is 

 not far below the surface, lime sinks and 

 deep ponds are common, and the surface 

 of the country is often uneven, occasionally 

 rugged ; but going southward one finds the 

 surface becoming gradually smoother until 

 it assumes the character of 'flatwoods.' 

 But these flatwoods are not necessarily low 

 lands, since in Baldwin and Mobile and in 

 the adjoining county of Florida (Es- 

 cambia) the land, where not lowered by 

 stream erosion, is from 150 to 300 feet 

 above tide. One of the most characteristic 

 features of this fiat land is the frequent 

 occurrence of shallow depressions which 

 are hardly ever more than four or five feet 

 deep, in which water may collect in shallow 

 ponds a fev/ yards to forty or fifty in 

 diameter. These are lined with a shrubby 

 growth of haw bushes, gum or cypress, 

 or sometimes of herbaceous plants only. 

 Other depressions, frequently of larger size 

 than those above mentioned, may be free 

 of water, thus giving rise to the sarracenia 

 fiats and to savannahs, covered with high 

 grass and supporting a sparse growth of 

 stunted long leaf pine. Along with the 

 prevailing grass are many bright-colored 

 flowers peculiar to the region, and the im- 

 pression is made upon the traveler that 

 he is in a well-kept park.' Lower lying- 

 lands timbered with long leaf and Cuban 

 pine are known as 'pine meadows,' in 

 which the shallow ponds are not so fre- 

 quent, but where the surface is gently un- 

 dulating and mostly clothed with a growth 

 of tall grass and flowers, like the savannahs. 



It is not easy to account for these shal- 

 low depressions; they are certainly not due 



to any underlying limestone near the sur- 

 face, nor is there, so far as we are aware, 

 any sufficient amount of soluble matters 

 in the soils to give rise to them. The only 

 explanation as yet suggested is that they 

 are due to the uneven surface of the under- 

 lying clayey beds of the formation, which 

 are reached almost everywhere in wells at 

 shallow depth. 



THICKNESS. 



The thickness of the formation is very 

 difficult to estimate. Dr. Hilgard long ago 

 observed that 'the position of the Grand 

 Gulf strata could rarely be shown to be 

 otherwise than nearly or quite horizontal 

 on an average, ' and during a recent trip by 

 Mr. Aldrich and myself in a skiff, from 

 Bucatunna to Merrill in Mississippi, a dis- 

 tance of fifty miles in direct line north and 

 south, we could discover no sensible dip in 

 the strata. Dr. Hilgard puts the thickness 

 at 250 feet, stating that in the absence of 

 deep borings in the gulf territory this can 

 be best observed on the northern edge of 

 the formation, where it forms high ridges, 

 from which there is an abrupt descent 

 northward into the level prairie country of 

 the Vicksburg territory. The deep borings 

 since made in the gulf territory have not 

 settled the question, for it is not as yet 

 possible to draw sharply the line between 

 the Grand Gulf and other strata there 

 penetrated. In Baldwin county, where 

 these beds come down to salt water at Mon- 

 trose on the eastern shore of Mobile Bay, 

 the blufi: itself is some 70 or 75 feet high, 

 and the level plateau, a mile or two back 

 from the bay, can not be less than 150 feet. 

 This is about the height of the Spring Hill 

 plateau at Mobile, and at the foot of that 

 ridge is the boring in which the Pascagoixla 

 bed is struck at about 700 feet. For the 

 first 180 feet of this boring the material 

 can not well be distinguished from Grand 



