186 Ed'dorial 'Miscellany. 



tensive lake, covering the eastern Miocene basin, and extending south- 

 wardly nearly to the Gulf of Mexico. The strata of this deposit are 

 cut through by the river Niobrara for two hundred miles of its course. 

 They are horizontal, light in color, and much more arenaceous than 

 those of the Miocene below. The upper strata consist of hard sand- 

 stones or calcareous grits, which wear but slowly, and hence still form 

 the great table-lands over much of the interior of the basin. Prof. 

 Marsh states that he has traced these high plateaux and the isolated 

 buttes from near the Black Hills south to the Arkansas river, and 

 found them all of the Pleiocene age. The fauna here indicates a 

 warm, temperate climate, and includes the mastodon, rhinoceros, cam- 

 els and horses ; remains of the latter being especially abundant. 



Acoustics. — Professor Tyndall contributes to the Contemporary 

 JRevieiv a paper of great interest on "The Atmosphere in Relation to 

 Fog-Signaling." He states that during the last ten years no less than 

 273 vessels have been lost on the British coasts, and estimates the loss 

 as far greater on the American seaboard, as the direct result of fogs 

 and thick weather. The ini ortance, therefore, of the efforts to find 

 an effective substitute for light in sound -signals to warn sailors ap- 

 proaching a dangerous coast can not be overestimated. With this view, 

 experiments were commenced in 1873, at the South-Foreland, near 

 Dover, with two powerful magneto-electric lights worked by steam 

 power, and trumpets, air and steam whistles. In addition to the appa- 

 ratus supplied by the British government, the Light-House Board of 

 our own country sent a steam-siren similar to those used in our light, 

 house system, and which he thus describes: 



"The princij^le of the siren is easily understood. A musical sound 

 is produced when the tympanic membrane is struck periodically with 

 sufiicient rapidity. The production of these tympanic shocks by puffs 

 of air was first realized by Dr. Robinson, and his device was the first 

 and simplest form of the siren. A stop-cock was so constructed that 

 it opened and shut the passage of a pipe 720 times in a second. Air 

 from the wind-chest of an organ being allowed to pass along the pipe 

 during the rotation of the cock, a musical sound was most smoothly 

 uttered. A great step was made in the construction of the instrument 

 by Cagniard de la Tour, who gave it its present name. He employed 

 a box with a perforated lid, and above the lid a similarly perforated 

 disk capable of rotation. The perforations were oblique, so that when 

 wind was driven through the lid, it so impinged upon the apertures 

 of the disk as to set it in motion. No separate mechanism was there- 

 fore required to turn the disk. When the perforations of lid and disk 



