359 



these, and of his numerous other works on geology, such as his 

 Western Islands and his Classification of Rocks. The influence 

 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, and a 

 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 1825. 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 1 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 



