HUGHES: ADAM SEDGWICK. 
259 
with water on the brain, but that light and heat had completely 
dissipated it. It is pleasant to read a good practical paper founded 
on original observation in which the character of dykes is so well 
discussed, as in Sedgwick's papers on the Phoenomena connected 
with Trap Dykes in Yorkshire and Durham. He refers them to an 
igneous origin, and points out that dykes are of all ages. 
In describing the columnar structure it did not escape his notice 
that the prisms were arranged at right angles to the cooling surfaces. 
He mentions also the common mode of weathering into great balls 
by the exfoliation of successive layers from the joint faces. 
He fully recognised the value of palgeontological evidence. As 
early as 1822 we find him in a letter to the Editor of the Annals of 
Philosophy, stating his view of " the importance of an intimate 
acquaintance with certain branches of natural history. Without 
such knowledge," said he, " it must be impossible to ascertain the 
physical circumstances under which our newer strata have been 
deposited. To complete the zoological history of any one of these 
formations, many details are yet wanting." 
He always carefully collected fossils and referred them to the 
best authorities he could find on each special group. But while he 
appealed to palasontological evidence, wherever he could, he recog- 
nised that the first thing was to get the rocks into the right order 
in the field. 
In the Annals of Philosophy, for April and July. 1825, Professor 
Sedgwick had a paper on the Origin of Alluvial and Diluvial For- 
mations, in which he distinguished the older formations, which we 
should now call drift, from the generally newer alluvial deposits. 
He pointed out the anomalous position and irregular distribution of 
the boulders, but the fact that glacial conditions once prevailed in 
our island and even extensive tracts all over the northern part of our 
hemisphere had not been recognised at that time. 
At the end of the paper is an appendix, giving an account of 
some changes in the channels which drain the fen-land : an account 
full of interest to those familiar with the Humber and its tributaries 
and all the phaenomena of silting up and warping. He concludes 
with this passage : — " If such extraordinary effects as those describ- 
