XXIV PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



tides are differently arranged in each. The alteration of the arrange- 

 ment in the latter case is such as would result from the rocks having 

 suffered a change of dimensions, been greatly compressed in a line 

 perpendicular to cleavage, and elongated to a certain extent in the 

 line of its dip. Of these changes there are evidences afforded also by 

 the diminution in the distance between any two points lying in the 

 line of pressure in contorted beds, the dimensions of the beds in dif- 

 ferent parts of contortions, the change in the dimensions of the organic 

 remains, and the arrangement of the green spots so generally seen in 

 Welsh slates, and resulting probably from original concretions. These 

 spots, Mr. Sorby remarks, in rocks without cleavage are almost per- 

 fect spheres, or are elongated in the plane of bedding. In cleaved 

 rocks they are like the minute particles compressed in a line perpen- 

 dicular to the cleavage, and more or less elongated in the line of its 

 dip. The result of Mr. Sorby' s inquiries is the strong support of 

 the mechanical theory of cleavage, and a confirmation of the observa- 

 tions of Professor Phillips and, partially, of the ^iews maintained by 

 Mr. Sharpe, from whom Mr. Sorby differs in maintaining that the 

 particles in general have suffered a change of position without actual 

 compressing or crystalline arrangement. Mr. Sorby maintains that it 

 is not possible to reconcile the mechanical facts noticed in his essay 

 with the supposition of an electrical action or other non-mechanical 

 agent being the efficient cause of the phaenomenou of cleavage. By 

 ingenious experiments he has been able to produce similar arrange- 

 ments of minute particles with those observed by him in nature, all 

 favourable to the theory which he so ably upholds. 



In the West Riding Geological Proceedings, Mr. Sorby has a paper 

 on the oscillation of the currents that drifted the sandstone beds of the 

 south-east of Northumberland, and on their general direction in the 

 coal-field in the neighbourhood of Edinburgh. By careful study of 

 the minuter characters of the drift-structure in sandstone, — more mi- 

 nutely and closely than has hitherto been done, — Mr. Sorby proposes 

 to arrive at definite results concerning the precise directions, charac- 

 ters, and velocity of the currents. The instances given in this essay, 

 which may be regarded as the prodromus of more extensive memoirs, 

 are most interesting, and warrant the conclusions at which he has 

 arrived so far. I am convinced that the path chosen by Mr. Sorby 

 is one of very great consequence to the future progress of geology, 

 and that by methods similar to those which I have advanced and put 

 in practice in the observation in the field of the distribution of organic 

 remains in strata, viz. the observation and careful noting of phseno- 

 mena, inch by inch, is as sure to yield valuable results to the purely 

 physical as to the natural-history observer. The smallest of facts is 

 not only worthy of notice and record, but may often prove to be the 

 key by which we are enabled to acquire a philosophical knowledge of 

 the rock-masses we are studying. The geology of no region, however 

 extensive or however limited, can be said to be done until its minute 

 as well as its more conspicuous constitution has been fully and fairly 

 made out. Hitherto this has rarely been attempted, and perhaps our 

 science is not yet ripe for an extensive employment of the m.ethod. 



