( 140 ) 



A little beyond the plain abovcmention* 

 ed appear fome tufas, which cover a long 

 and fteep declivity defcending into the fea, 

 and beyond the tufas we again meet with 

 lavas forming broad currents. Thefe lavas 

 have the horn-ftone for their bafe, and their 

 external charaderiftics are the following : 



They are light, extremely porous, and 

 therefore eafily penetrable by water 5 they 

 with difficulty give fparks with fteel, which 

 breaks off fragments at every ftroke. They 

 feel rough under the finger, and emit an 

 argillaceous odour. They contain nume- 

 rous feltfpars, which are confpicuous from 

 their whitenefs, on a dark red ground ap- 

 proaching to a black. Some fhew a degree 

 of calcination which they have fufFered in 

 the fire, and are, in confequence, eafily 

 crumbled. Others have fuffered no injury ; 

 and the difference obfervable in them is 

 rather to be afcribed to the difference of 

 the nature of the feltfpars, than to their 

 liaving fuffered a greater degree of heat, 

 the lava in which they are both incorporated 



appearing 



