Correspondence — Mr. Alfred Harlcer. 431 



If the drifts were not frozen, I cannot understand tlie production 

 in tliem of overfolds of considerable horizontal extent (such as that 

 shown at the south end of Mr. Green's pit), without any obliteration 

 of the planes of deposition. 



Mr. Jukes-Browne speaks of the drifts as being pushed along in a 

 ' partially-frozen state.' Even if contortion can be produced by coast- 

 ice in deposits under such conditions, I cannot conceive that the order 

 of succession of the deposits should be so constant as it is in the 

 Sudbury area, upon this hypothesis. Surely the incoherent portions 

 of the drift would become churned up, so that we should find masses 

 of boulder-clay, gravel, and loam mingled together, and having 

 their divisional planes oblitei-ated. I have seen no signs of such in 

 the area under consideration. 



In asserting that contortions occur " in the accumulations which 

 lie on the summits of ridges," I iised the term ' summits ' not for the 

 highest points, but for the upper portions of the major ridges, and I 

 referred to Mr. Green's pit and the pits near the cemetery. These 

 pits are situated at the upper parts of major ridges, and the contor- 

 tions are seen in Mr. Green's pit to lie against a minor ridge. At the 

 same time I do not wish to assert that all the contortions were caused 

 by the inequalities close to which they now lie. 



I regret that my summing up should appear biassed in favour 

 of one explanation. I visited the Sudbury area with little practical 

 knowledge of the East Anglian drifts. Having read much of the 

 literature bearing upon these drifts, including Mr. Jukes-Browne's 

 lucid papers, I started my examination with a strong bias in favour 

 of their marine origin. As I was gradually led to abandon this view, 

 I considered it worth while to state the evidence which weighed 

 with me, but brought forward my reasons as an advocate, and not as 

 a judge. I should certainly not venture to make a charge to a jury 

 with the evidence derived from so limited an area. 



I take this opportunity of calling attention to one or two inaccu- 

 racies in Fig. 1 of my paper. The Crag mass C should be separated 

 from the filled-in ground D by a little gravel; the junction of the 

 Thanet sand and chalk in the isolated patch at the south end of the 

 pit should be in the same straight line with that of the main portion, 

 and the top and base of the Thanet sand layer are much more even 

 than represented in the diagram. John E. Maer. 



St. John's Coll., Cambridge. 

 Aug. 6, 1887. 



THE CORTLAND ROCKS. 

 Sir, — Dr. Callaway, in combating the ' metamorphio ' origin of 

 the rocks of the 'Cortland Series,' does not appear to be aware that 

 Prof. Dana has materially modified his earlier opinion on this point. 

 After examining some new i-ailway cuttings, he was convinced that 

 the hornblendic and augitic rocks are of true eruptive origin, and 

 although he does not find that the new sections throw any light on 

 the origin of the 'soda-granite,' his former line of argument is 

 evidently much weakened (Amer. Journ. Sci. 3, vol. xxviii. p. 3S4:,. 



