Origin of Movements in the Earth's Crust. 141 



(c) Ostrea deltoidea and Gryplma dilatata occur together in 

 these clays, and also in the Corallian, but in no other forma- 

 tion. 

 The zones 2, 3, and 4 are of Lower Kimeridge Clay age. The 

 lowest zone (2) is very persistent in character, and is met with in 

 Yorkshire, Cambridgeshire, Oxfordshire, and the south of England. 

 The remaining zones (3 and 4) are local in their development. 



3. " Origin of Movements in the Earth's Crust." By James K. 

 Kilroe, Esq. 



The author is convinced that a very important factor has been 

 omitted from the usual explanation offered in accounting for the 

 vast movements' which have obtained in the Earth's crust. His 

 acknowledgments are due to Mr. Pisher for the extensive use 

 made of his valuable work. He also refers frequently to the views 

 and publications of other writers on terrestrial physics. Erom a 

 somewhat conflicting mass of figures he concludes that about 20 

 miles would remain to represent the amount of radial contraction 

 due to cooling during the period from Archaean to Recent times, 

 corresponding to a circumferential contraction of 120 miles. This 

 will have to be distributed over widely separate periods, at each of 

 which there is abundant evidence of lateral compression. 



But he considers that this shrinkage alone will not account for 

 all the plication or distortion of strata which constitute so im- 

 portant a factor in mountain-making, and he is disposed to supple- 

 ment it in the way to which allusion has already been made by 

 Mr. Wynne in a recent Presidential Address, viz. by considering the 

 effects of the attenuation of strata under superincumbent pressure 

 from deposition in subsiding areas, which involves the thickening, 

 puckering, reduplication, and piling up of strata in regions where 

 pressure has been lessened. It should be noted that, until disturb- 

 ance of " cosmical equilibrium " takes place, mere pressure does not 

 produce metamorphism. The extent of these lateral movements is 

 described, and it is asserted that the theories hitherto adopted to 

 account for plication, &c. are inadequate. 



The origin of the horizontal movements is further discussed on 

 the hypothesis that solids can flow after the manner of liquids, 

 when they are subjected to sufficient pressure. He considers that 

 the displacement in N". W. Scotland may have been initiated by the 

 force due to contraction and accumulating in the crust throughout 

 the periods marked by the deposition of Torridon Sandstone and 

 Silurian strata, the elements of movement finding an exit at the 

 ancient Silurian surface. In this case the pile of Silurian strata 

 formerly covering the region now occupied by the North Sea and 

 part of the Atlantic forced the lowest strata to move laterally, the 

 protuberances of the underlying pre-Silurian rocks being also 

 involved in the shearing process. Similar results obtain in other 

 mountain areas. The strata compressed have been greatly attenuated, 

 and extended in proportion ; in this way we may account for the 

 piling up of strata by contortion in certain regions. The connexion 



Phil Mag. S. 5. Vol. 28. No. 171. August 1889. M 



