9(5 



MB. W. A. BICHABDSON 0> T THE PETBOLOGY [vol. lxxix, 



facts of distribution "are shown in the vertical section AB, on the 

 left of rig. 9. This section is, however, diagrammatic, for only 

 sufficient bands could be inserted to show the relative distribution. 

 If the curve and the section be compared with those for Creta- 

 ceous flint or Liesegang gels, 1 it will be seen that the limestone 



Fig. 9. — Vertical distribution of nodular limestone 

 in the Lias of Dorset. 



600 



A-00 



500 



200 



i" Distance- apart o\ Eand<> 



B 



'O 



2o 



50 <K> 



50 



distribution is of the same type. The rhythm may be anabysed as 

 follows : — 



(1) In the lower 100 feet, the mean separation of bands is 1 foot, and 



the maximum 3 feet. 



(2) The next 200 feet show (in one case only) a minimum interval of 



4 feet, and a mean of about 10. 



(3) In the remaining- 300 feet to the top of the Middle Lias, the minimum 



separation is 12 feet, and the mean about 20 feet. 



1 W, A. Richardson, Geol. Mag-. 1919, p. 541. 



