$14 Geological Society. 
my present limits were I to attempt to give a general analysis of 
these, and of his numerous other works on geology, such as his 
Western Islands and his Classification of Rocks. The infiuence 
exerted by them on the progress of our science has been powerful 
and lasting, yet they have been less generally admired and studied 
than they deserve. Their popularity has been impaired by a want 
of condensation and clearness in the style, a defect which no one 
could more easily have remedied than the author, had he been 
willing to submit to the necessary labour. Another blemish has 
also contributed to give a repulsive character to some of his later 
productions, especially his System of Geology, the absence, or ap- 
parent absence, of all enthusiasm and love for his subject, anda 
disposition to neglect or speak slightingly of the labours of others, 
and even to treat in a tone bordering on ridicule some entire depart- 
ments of science connected with geology, such as the study of fossil 
conchology. I attribute these imperfections principally to habitual 
ill health acting upon a sensitive mind, for certainly, Dr. MacCul- 
loch’s spirits were much depressed by bodily sufferings when I 
had first the pleasure of knowing him, about the year 1822. His 
imagination was then haunted with the idea that his services in 
the cause of geology were undervalued, and it was in vain to com- 
bat this erroneous impression. After that period he almost entirely 
withdrew himself, even when residing in London, from all personal 
intercourse with the most active geologists; and to those who knew 
him this seclusion from scientific society was a subject of frequent 
regret. Having expressed myself thus unreservedly on some of the 
peculiarities and defects of his style, I may affirm that as an origi- 
nal observer Dr. MacCulloch yields to no other geologist of our times, 
and he is perhaps unrivalled in the wide range of subjects on which 
he displayed great talent and profound knowledge. For myself I 
may acknowledge with gratitude that I have received more instruction 
from his labours in geology than from those of any living writer. 
One of the most important communications which we have re- 
ceived for many years is an essay by Professor Sedgwick on the 
changes of structure produced in stratified rocks after their deposi- 
tion. Respecting the magnesian limestone, he has confirmed by 
new arguments the conclusions which he formerly drew, in proof 
that the complicated concretions of this rock have been pro- 
duced since the original deposition of the beds. But the principal 
part of his memoir is devoted to the description of the cleavage or 
slaty structure of rocks, and those partings which have been called 
joints. The author first shows the analogy of the Cumbrian zone of 
green slate and porphyry with the structure of the principal chain 
of North Wales. In these regions, as in part of the slaty series of 
Westmoreland and Lancashire, occur many beds exhibiting a slaty 
cleavage, which the Professor distinguishes from a jointed structure. 
Joints, he says, are fissures placed at definite distances from each 
other, the masses of intervening rock having no tendency to cleave 
in a direction parallel to such fissures: whereas in the planes of 
cleavage, the rock is capable of indefinite subdivision in a direction 
