172 



Now, then, which of all the planes are the planes of dip? Dr- 

 Boase, like the Woodwardian Professor, selects those which run 

 with the laminae, and yet the layers of massive crystalline and 

 granitic rocks often lie the other way. But this seems to be very 

 much a matter of taste ; different observers selecting for the scene 

 of their measurements different planes. Some pay great attention to 

 the laminae, others neglect them ; nay, the same observer shall some- 

 times select as strata one series of planes, sometimes another. 



Professor Phillips, in a passage which is too long to be quoted, 

 has expressed the same idea in language equally expressive. 



Dr. Boase presents to those who differ from him on this subject 

 the following alternative : either Stratification implies a successive 

 deposition of sedimentary matters held in suspension, in which case 

 none of the frimary shisti are stratified \ or merely parallel planes 

 without regard to the cause of their production, in which case not 

 only the 'primary shisti are stratified bid granite also. 



in the thirteenth chapter will be found some excellent observations 

 on the nature of Inclined Strata, tending to show that these last are 

 not necessarily the effect of disturbance, but are to be attributed, in 

 the Primary Slates, to original structure, and in many of the Second- 

 ary, partly to this cause, and partly to deposition upon inclined sur- 

 faces. 



The difficulty I have been considering is by no means confined to 

 Primary Slates. Mr. Conybeare has observed on the coast of Sully, 

 in Glamorganshire, that the Lias splits spontaneously into blocks of 

 regular figure, corresponding to ihat of a ciystal of calcareous spar. 

 If this be the case, where are we to look for the seams of Stratifica- 

 tion ? I have felt for very many years, and I still feel that the 

 indistinctness of this term is one of the most dangerous stumbling 

 blocks we have to encounter. If we would found upon this distinc- 

 tion the grand classification of rocks into Neptunian and Plutonic, 

 surely we ought to have some test by which to determine whether 

 rocks are stratified or not. If, looking to the theory of M. Elie de 

 Beaumont, we would know whether strata are conformable or dis- 

 turbed, surely we ought to be placed in a condition to determine 

 what Strata are. On taking leave, as I must do, of Dr. Boase's work, 

 I again recommend it to your attentive perusal ; it is written with 

 great candour as well as earnestness, and will be found a useful cor- 

 rective of many opinions which appear, to me at least, to have been 

 too inconsiderately adopted. 



Mr. De la Beche, one of your Vice-Presidents, to whose pen and 

 pencil our science has been for a series of years continually and largely 

 indebted, has pubhshed a small volume, entitled " Researches in Theo- 

 retical Geology". The main tendency of this volume is to establish 

 the importance and practicability of subjecting geological opinions to 

 the tests of chemistry and natural philosophy. The Author goes over 

 much ground, keeping always the same direction, having apparently 

 no other objects in view than the acquisition and communication of 

 sound knowledge, the detection and exposure of error, and the disco- 



