26 



Experiments with and phenomena of vacuum tubes. By R. A. Fessenden. 



The electro-magnetic inertia of a large magnet, By Thos. Gray 



Some new electrical apparatus. By R. A. Fessexdex. 



<)x the construction and use of a bolometer. By B. W. Snow 



Rotary blowers. By John T. Wi 



An inquiry as to the cause of variety in rock deposits us seen in Hudson 



RIVER BEDS AT RICHMOND, InIi. I!y JOSEPH MOORE. 



Take a depth of our bed rock at this place of, say fifty feet, along the 

 river channel. The variations in the lithological character of the numer- 

 ous sharply defined layers is very marked and very many times repeated; 

 not more so, however, than in hundreds of other localities throughout the 

 country at the same or at other horizons. Here the well solidified por- 

 tions are thick-bedded (the layers say a foot thick) while not far below or 

 above they are thin, say one or two inches. These consolidated layers 

 vary in texture and composition, some of them being nearly pure lime- 

 stone and sufficiently crystalline to take a fair polish. < >thers are masses 

 mainly of brachiopods, often well preserved and matted together with 

 clay or with lime and iron from a state of solution. Others still are shoals 

 of commingled sand, clay and lime and almost destitute of fossils. Then 

 there are the intercalated beds of clay with sufficient calcium carbonate 

 to effervesce with acids for a little while, but leaving their principal bulk 

 when the solvent has done what it can. These beds of finest grained clay 

 vary in thickness from a very few feet to a few inches and even to the 

 thickness of ordinary paper. Often these clay deposits are entirely desti- 

 tute of fossils and again they are the hope of the hunter of trilobites and 

 a few other form that may be found therein. All these features are fa- 

 miliar to the observer in various localities. 



But the commonness of the phenomena does not make their causes the 

 less desirable to seek. It can hardly be supposed that the ocean varied in 



