74 SECTIONAL ADDRESSES, 
happened was the production of a vitreous cement, consisting of silicates 
of alumina and the alkalis, sufficient to bind together the sand grains. 
We are reminded of the fused Torridon sandstone that is found at the 
margins of Tertiary dykes in the western isles of Scotland, but in these 
the alkali was furnished by the felspar originally present in the sand- 
stone. This paper probably contains the last expression of the pure 
Huttoniaa philosophy. Hall was now the sole survivor of the original 
group who established the Huttonian theories. | Having begun as an 
innovator and a radical, regarded askance for his revolutionary tenden- 
cies, he was now a conservative holding fast to orthodox opinions, even 
when they were out of date. His passion for experiment lasted to 
the end, and he seems to have maintained his furnace in working 
order for over forty years. He died in 1832. Although he was 
not the greatest of the trio—Hutton, Playfair, and Hall—whe 
founded modern geology, he was worthy to take his place with the 
others. -Hutton’s was the original master-mind who, by sheer induc- 
tion and abstract reasoning, had read the secrets of the earth. Playfair 
was the man of balanced judgment who grasped the essentials and 
placed them in convincing clearness before a sceptical public. Hall 
had his special field of work in which he excelled all his contemporaries, 
and for us who are watching with profound interest the rapid progress 
of expérimental investigation into geophysical and _ petrophysical 
problems, it is not uncongenial to pay a tribute to his memory. 
