Address of the President of the Royal Society. 109 
which to this day holds its high place in the estimation of geologists as 
the foundation of our knowledge of this impartant class of deposits, 
whether we regard their origin, form of deposition, peculiarities of struc- 
ture,-or organic contents. 
ontemporaneously with this excellent work, he examined the whin 
sill of Upper Teesdale, showed its claims to be treated as a rock of fusion, 
and discussed the perplexed question of its origin, 
Advancing to one of the great problems which occupied his thoughts 
for many years, he combined in 1831 the observations of the older rocks 
of the Lake mountains which.he had commenced in 1822, and added a 
vided honor of the first unrolling of the long series of deposits which 
constitute the oldest groups of British fossiliferous rocks, ; 
Still more complete, however, was the success of that work which 
was undertaken immediately afterwards on the coeval roc of Wales; 
by which Professor Sedgwick and Sir Roderick Murchison, toiling in sep- 
arate districts, unravelled the intricate relations of those ancient rock 
and determined the main features of the successive groups of ancient life 
which they enclose. These labors began in 1831-32, and in 1835 the 
two great explorers had advanced so far if their research as to present a 
united memoir to the British Association in Dublin, showing the progress 
each had made in the establishment of the Cambrian and Silurian sys- 
tems, as they were then called; Professor Sedgwick taking the former, 
and Sir Roderick Murchison the latter for his special field of study. 
In 1843 Professor Sedgwick produced two memoirs on the structure of 
ing principally taken from his observations in 1831-82, while the more 
detailed sections of the eastern part were from those of 1842-43. 
These two papers gave the complete outline or framework, as it were, of 
the geological structure of this intricate region. In several subsequent 
