HUTTON. 229 



employed In the prosecution of chemical experi- 

 ments. In one of these he made an interesting 

 discovery which relates to the changes that go on 

 in apparently most unchangeable rocks, and which 

 are due to the action of percolating water on them. 

 He noticed that in the midst of dense masses of 

 hard, cold, volcanic rock, called basalt, crystals of 

 great beauty are found in cavities. They can be 

 fused under the blowpipe easily, and that is not 

 the case with the surrounding rock. On adding 

 hydrochloric acid to one of these zeolites, as they 

 are called, a gelatinous substance is formed out of 

 the crystal, and on evaporation, sea salt or chloride 

 of sodium is found. "This was the first instance," 

 writes his biographer, Playfair, "of an alkali 

 being found in a stony body." He went to Cheshire 

 to see the salt mines, went to Birmingham, and 

 then set out for Wales. His desire was to trace 

 the hard gravel of granular quartz which is found 

 in such abundance in the soil about Birmingham 

 and elsewhere, to its origin, and to find out whence 

 it came and how it was distributed. He found 

 none of the- rock in Wales ; but on returning he 

 found it in places, in a body of old rocks which 

 stand out of the country between Bromsgrove and 

 Birmingham. 



Then Hutton wrote a little book on the "Nature, 

 Quality, and Distinction of Culm and Coal." The 

 result was more economical than scientific, for it 

 led to the abolition of a duty on the small coal of 

 Scotland. He read hard, and Qvery book on travels 



