persevering, observant, and truly logical in his method of thought, Hutton was accumulating facts upon which to reason in geology, whilst the so-called geologists of the day were forming theories without facts. He took a tour to the north of Scotland, through Ross and Caithness, and returned by way of Aberdeen to Edinburgh, and he studied the mineralogy and geology of the districts. Returning home, he still went on farming, and at the same time he became a partner with his friend Davie in a manufactory of ammonia. By the year 1768, being forty-two years of age, Hutton had matured his plans; he let his farm at a very advantageous rent, and, untroubled about his affairs, having his three sisters as his companions, he went to Edinburgh, and entered the singularly interesting scientific society of that time. His biographer, Playfair, writes that Hutton, “employed in maturing his views and studying nature with unwearied application, now passed his time most usefully and agreeably to himself, but in silence and obscurity with respect to the world.” “Free from the interruption of professional avocations, he enjoyed the entire command of his own time, and had sufficient energy of mind to afford himself continual occupation.” A good deal of his leisure was now employed in the prosecution of chemical experiments. 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.