642 Transactions of the American Institute. 



segments of glass surroundiug the central flames, "vvhose focal rays 

 are parallel, and horizontal in direction. In tixed lights the deflec- 

 tion is only in meridian planes, the natural divergence in azimuth 

 beiiig unaltered; but in the revolving lights the focal rays are 

 gathered into a number of cylindrical beams, each of which, 

 by the rotation of the apparatus, are brought to the eyes of an 

 observer. 



NEW JERSEY MARL. 



The remarkable deposit of green sand, misnamed marl, extend- 

 ing from the Atlantic ocean, near Sandy Hook, for many miles, in 

 a southwest direction, is now very extensively used as a fertilizer. 

 It contains but very little of the constituents of ordinary marl, that 

 is to say, carbonate of lime and silicate of alumina; however, por- 

 tions of the great marl district designated as yellow marl, consist 

 mainly of carbonate of lime. The green sand varies in its compo- 

 sition in diflferent localities. That in Monmouth county, particu- 

 larly in the Squaukum district, contains the largest percentage of 

 phosphoric acid. About one-half its weight consists of silica or pure 

 sand, nearly one-fifth of protoxide of iron, one-tenth of water and 

 organic matter, and one-twentieth of alumina and magnesia. The 

 remaining fifteen per cent embraces, according to the analysis of 

 Prof. Eaton, 7.2 per cent of potash and soda; 3.3 lime; 4.54 phos- 

 phoric acid; .34 sulphuric acid; .32 soluble silica. In relation to 

 the more essential constituents, this analysis agrees with that by 

 Prof. Cook, of Rutger's College, the State Geologist. 



The eflect of Monmouth marl on sandy soils is strikingly dis-. 

 played at Long Branch. In front of the Continental Hotel, and 

 within twenty-five rods from the ocean, is now to be seen a luxuriant 

 growth of grass, partly the result of marl. Green sand is said to 

 have wonderfully stimulated the potato crop in Monmouth county. 

 Lands which were formerly thought unworthy of cultivation have, 

 by the application of this fertilizer, been transformed into the most 

 fruitful and productive portions of New Jersey. Farmers flock 

 from all directions to the marl pits, and it is said not less than 

 eighteen hundred wagon loads have been collected in a single day. 



The facilities for procuring the green sand have been greatly 

 increased by the construction of the Raritan and Delaw^are Bay 

 railroad, from which a branch now extends to the works of the 

 Squankum Marl Company. Here the marl is found in the bed of a 

 tributary of the Manasquan river, about ten feet below the surface. 

 Through the energy and foresight of Mr. O. B. Kinney, all the 



