E. A . Smith — Post-Eocene Formations of Alabama. 285 



ful beats which become more and more frequent as the 

 velocity of rotation of the disk is increased till, with a certain 

 velocity, the beats blend into a smooth continuous sound, 

 which is that given by the fork when held near its proper 

 resonator. This sound of UT 3 as given by the blending of its 

 interrupted sound is, however, accompanied by another and 

 graver sound ; but the existence of this additional sound does 

 not interfere with the neat perception of the blending of the 

 interrupted sound of UT 3 . With this apparatus the blend- 

 ing of interrupted sounds has been shown to the entire satis- 

 faction of a large audience. 



To enable one readily to make the apparatus the following 

 dimensions are given. The diameter of opening of mouth of 

 flask is 3 cms . Depth of flask 16'25 cras . Capacity of flask, in- 

 cluding tube, T, is 483 cub cms - 



In the ligure the rotator, R, is shown driven by a cord. It 

 is necessary, if an accurate determination is to be made of the 

 duration of the residual sensation, to drive the disk by gearing 

 as is done in the apparatus I have used. When the disk is 

 driven by a cord one can show the blending of interrupted 

 sounds, but an accurate determination of the duration of the 

 residual sensation is prevented by the friction which exists 

 between the flange of JB and the disk, though the surfaces of 

 these are coated with a fllm of oil. 



Art. XXVI. — The Post-Eocene Formations of the Coastal 

 Plain of Alabama ; by Eugene A. Smith, University of 

 Alabama. 



The succession of the Post-Eocene formations of the Coastal 

 Plain of Alabama as brought out by the work of our Geo- 

 logical Survey, is in descending order, as follows : 



Quaternary. 



Recent and Pleistocene. 



1. Soils, and rain wash, River alluvium, and Coast formations 



(Riloxi). 



2. Mobile Bay formation, Second Terraces or Second Bottoms of 



the rivers, and the mantle of Ozark or Geneva sands. 



Of undetermined Classification. 



The Third, or Main River Terraces, and the Lafayette mantle of 

 pebbles, sands, and loam. (The Lafayette is by some con- 

 sidered as Pre-glacial Pleistocene, by others as late Pliocene.) 



