80 Revieii-8 — T. Mellard Eeade — Earth Structure. 



(1) its interioi' spheroid or nucleus, "considered by many pbysicists- 

 to be mainly iron," (2) a 500-mile zone or shell of igneous magma, 

 and (3) the lithosphere, 30 miles thick. The ten-mile zone of 

 elevation and depression is shown by a strong line ; within it " all 

 the denudations, depositions, depressions, and elevations of the 

 surface of our planet take place." A diagram of this kind is always- 

 useful. We have one before us now, printed in 1851, by James 

 Nasmyth. It represeiits an arc of a circle 64 feet in diameter on 

 which are indicated the relative magnitude of several mountains, 

 the deepest mine, and the probable mean elevation of dry land. 

 Nasmyth rightly remarked that " In contemplating Geological 

 Phenomena, nothing more directly aids the mind in arriving at 

 correct conclusions than the useful practice of comparing the 

 magnitude of all such phenomena to that of the Earth itself." 



Mr. Mellard Eeade starts with the recorded instances of elevatioiv 

 and depression, making special though brief reference to those of 

 Pleistocene and later times, such as Raised beaches. Submerged 

 forests, and 'Drowned valleys.' These in some cases may have 

 been contemporaneous ; the 40 ft. beach at Irvine, in Ayrshire, 

 being linked with a 10 ft. beach in the Isle of Man, and with 

 a depression on the shores of the Bristol Channel. In other cases 

 the evidence of ' raised beaches,' which indicate a former submersion 

 of four or five thousand feet, requires confirmation. 



Admitting movements of 1,000 feet, the author proceeds to show 

 that these oscillations of level cannot be due mainly to the shifting 

 of weight by denudation and sedimentation, though such changes 

 exert influence in combination with other agencies. He believes 

 that the relative proportions of land and water have been fairly 

 constant throughout the ages, and that regional changes of level 

 are due to alterations in the bulk of certain portions of the lithosphere 

 without movement in mass. 



The researches of various observers on the difi"usion of metals, 

 the difierentiation of igneous magmas, the effects of temperature 

 and pressure, and the change of physical properties and of volume 

 with changed conditions, show that " the conception of the earth 

 simply as an fi/eri mass cooling in space is a fallacious one." 



In his " Origin of Mountain Ranges " the author maintained that 

 as the volcanic pipes from which lava emissions proceed are probably 

 in communication with the subterranean heated matter, there would 

 necessarily be some mixture of material differing in constitution and 

 thermal condition. Consequent upon internal changes, the volume* 

 and specific gravities of the mineral masses of the lithosphere would 

 be subject to increase and decrease over large sections of the 

 globe. Increase of volume by expansion would lead to continental 

 uplifts, while the ' deeps ' of the ocean would be depressions below 

 the true spheroid, due to the superior density and less volume of 

 the underlying masses of the earth. 



On the other hand, the expansions and contractions to which 

 mountain-building is due " are mostly lateral and intermittent, 

 creating creeps of the lithosphere and surface rocks, ending in the 



