12 THE DONCASTER EARTHQUAKE OF 1905. [Feb. I906, 



paper, 1 is due to the differential growth of a crust-fold along a fault 

 which intersects it transversely. As a general rule, the first move- 

 ment is a rotation of the middle limb accompanied by the almost 

 simultaneous slip of the two arches, and followed after an interval, 

 which is usually brief, by a shift of the middle limb. The move- 

 ments, in which the Doncaster earthquake originated, presented a 

 slight variation in order. They consisted of successive, but con- 

 tinuous, displacements, first of the south-western arch, then of the 

 middle limb, and finally of the north-eastern arch. 



EXPLANATION OP PLATE II. 



Map illustrating the area affected by the Doncaster earthquake of April 23rd, 

 1905, on the scale of 25 miles to the inch. 



1 ' Twin-Earthquakes ' Quart. Journ. Geol. Soc. vol. lxi (1905) pp. 18-33. 



