THE ROYAL DUBLIN SOCIETY 155 



necessary that larger quantities should be sent up for 

 investigation. This clay had been discovered by 

 Donald Stewart. In 1791, Stewart announced that he 

 had found in the county of Waterford a very valuable 

 clay fit for glasshouse pots. 



When making a tour through the county Longford 

 in 1794, he found several valuable quarries of flags, 

 slates, and fine variegated marble, on the estates of Lord 

 Oxmantown and Mr. Shuldham, near Ballymahon. 

 During this year, Stewart was directed to make a de- 

 scriptive catalogue of the minerals, fossils, clays, &c, dis- 

 covered by him, and deposited with the Society, and to 

 label the collection. In 1 799, he proceeded to Banbridge 

 to search for coal, and he had to experiment for mines 

 on the estates of Morley Saunders and F. W. Greene 

 in the county of Wicklow. On one occasion, he laid 

 before the Society samples of marble raised from the 

 quarries of the Marquis of Hertford, in the county 

 of Antrim, which was said to be of excellent quality and 

 to bear a fine polish. He was also paid for quarrying 

 and drawing away specimens of various pillars and 

 marbles from the Giant's Causeway, &c, to Port Ballen- 

 trae, for the Society. In November 1797, Stewart was 

 directed to go to the island of Rathlin, to examine if it 

 yielded any stratum of Terrass, General Vallancey 

 having informed the Society that some of that sub- 

 stance, equal to any imported from Holland, had been 

 found there. Soon after, Mr. Joseph Allen informed 

 the Society that he had found immense quantities of 

 7 err ass and Terra Pozzuolana 1 at Larne. When 

 Stewart had completed a good deal of his work, Dr. 

 Percival was invited to advise as to the arrangement 



1 Terrass and Pozzuolana are soft ferruginous tufas, that possess 

 the property of consolidating when mixed with a portion of lime, and 

 employed as cement. 



