." Notices of Memoirs^Prof. La.pic'ortJl's Address. 475 



those of the one and the symmetry of those of the other. In the geology of the 

 earth-crust, also, the inter-crossing of the two sets of folds, theoretically at riglit 

 angles to each other, gives rise to effects equally startling. It lies at the origin 

 of the thrust-plane or overfault, where the septal region of contrary motion in the 

 fold becomes reduced to, or is represented by. a plane of contrary motion. It 

 allows us to connect together under one set of homologies folds and laults. The 

 downthrow side of the fault answers to the trough, the upthrow side to the 

 arch, of our longitudinal fold, while the fault-plane itself represents the septal area 

 reduced to zero. The node of the fault, and the alternation and alteration of 

 throw, are due to the effects of the transverse folding. 



These transverse folds of different grades, which affect the various layers of the 

 earth-crust differentially, account also for the formation of laccolites, of granitic 

 cores, and of petrological provinces. They enable us also to understand many of 

 the phenomena of metamorphism. 



Of the folds of the third order, I shall here say nothing, but I must frankly 

 admit that the primal cause of all this tangential movement and folding stress is 

 Still as mysterious to me as ever. I incline to think that the motion is due to 

 many causes— to tidal action, to sedimentation, and many others. I cannot deny, 

 however, that it may be mainly the result of the contraction in diameter of our 

 earth, due to the loss of its original heat into outer space ? For everywhere we 

 find evidences of symmetrical crushing of the earth-crust by tangential stresses. 

 Everywhere we find proofs that the various layers of that crust have been most 

 affected differentially, and the outer layers have been bent the most. We seem 

 to be dealing not so much with a solid globe as with a globular shell composed 

 of many layers. 



Is it not just possible after all that, as others have suggested, our earth is such 

 a hollow shell, or series of concentric shells, on the surface of which gravity is at 

 a maximum, and in whose deepest interior it is non-existent? May this not be 

 so, also, in the case of the sun, through whose spot-eddies we possibly look into 

 a hollow interior ? If so, perhaps our present nebulse may also be hollow shells 

 formed of meteorites ; on the surfaces of these shells the fiery spirals we see 

 would be the swirls which answer to the many twisting crustal septa of the 

 earth. Our comets, too, in this case might be elongated ellipsoids, whose visible 

 parts would be merely interference phenomena, or sheets of differential movement. 



In this case we have represented before us to-day the past of our earth as well 

 as its present. Uniformity and Evolution are one. 



Thus from the microscopic septa of the laminse of the geological formations we 

 pass outwards in Jact to these moving septa of our globe, marked on the land by 

 our new mountain chains, and on the shores by our active volcanoes. Thence we 

 sweep, in imaginatioii, to the fiery eddies of the sun, and thence to the glowing 

 swirls of the nebulae ; and so outwards and upwards to that most glorious septum 

 of all the visible creation, the radiant ring of the Milky Way. 



Professor George Darwin, in his Address to the section of Mathematical and 

 Physical Science at the meeting of the British Association at Birmingham in 1886, 

 with all the courage of genius, and the authority of one of the sons of the prophets, 

 acknowledged that it seems as likely that ' ' meteorology and geology will pass the 

 word of command to cosmical physics as the converse.^' Behind this generous 

 admission I shelter myself. But I feel absolutely confident that long after the 



f)hysicists may have swept away these astronomical suggestions as " the baseless 

 abric of a vision," there will still remain in the treasure-house of the geological 

 fold a wealth of abundant material for the use of the mathematician, the physicist, 

 the chemist, the mineralogist, and the astronomer, of the deepest interest and of 

 the highest value. 



Note. — The first Part of the above Address was set up inadvertently from an 

 uncorrected proof. Most of its errors explain themselves, but for the sake of 

 clearness, the reader should substitute the following for the corresponding 

 paragraphs on pp. 420-421. 



In the earlier days of geology one of the first points recognised by our strati- 

 graphists was the fact that the formations were successive lithological sheets, whose 

 truncated outcropping edges formed the present surface of the land, and that these 

 sheets lay inclined at an angle one over the other, as WiUiam Smith quaintly 



