20 HjSTORr of the SOCIETT. 



cavities in the interior of the bafaltic rocks on this coaft, though 

 they are frequent on the furface expofed to the air. 



The laft variety of whinftone enumerated by Dr Richard- 

 son is the Ochrous, which makes, as he fays, a confpicuous figure 

 in the ftupendous precipices along the coaft of Antrim. It is dif- 

 pofed in extenfive ftrata of every thicknefs, from an inch to 

 twenty-four feet, and varies in colour, from a bright minium 

 to a dull ferruginous brown. 



Three remarks are made by Dr Richardson, that are un- 

 doubtedly of importance, and fhow that this ftone is merely 

 bafalt in a certain flate of decompofition. 



1. The ochrous ftrata are extenfive ; they remain always pa- 

 rallel to the bafalt ftrata which they feparate ; they unite to the 

 bafalt without interrupting its folidity ; the change from the 

 one to the other is fudden, and the lines of demarkation are di- 

 ftindl. The ochrous ftone is never found but contiguous to 

 other bafalt, 



2. The fubftances imbedded in the ochrous rock, and in ba- 

 falts, are exadlly the fame ; calcareous fpar, zeolite, chalcedony, 

 &c. 



3. Among the varieties which this rock prefents, there may 

 be found every intermediate ftage between found bafalt and 

 perfecft ochi'e. The change is often partial, beginning with 

 veins and flender ramifications. 



ALGEBRA. 



1800. Rule for reducing to a Continued Fraction the Square Root of 



uil^forrtdJ- ^"y given Integer Number, not a Square. By James Ivory, 



Efq. Communicated loth January 1801. 



I. Let N be the given integer number, and take « the root of 



the fquare next lefs than N ; and, for the fake of uniformity, 



put ?' = I, R°=o, /* = «. 



2. Take 



