Page:The Geologist, volume 5.djvu/55

Rh instance, with the exception of the Northamptonshire beds, which have been carefully noted by my friend, the Rev, A. N. Griesbach, I have visited the localities given in this work," but in no part of that monograph has my friend referred the Northampton Sands to the lias. Mr. Macalister has been therefore altogether misinformed on this subject. I submit that it ought to be a rule with gentlemen furnishing papers to the valuable pages of the 'Geologist,' in every case to refer to the original articles from which they quote. Yours most truly, 2em 

—The generally accepted subdivisions of the chalk are,—1, Upper White Chalk with bands of Flint nodules; 2, Middle or Lower White Chalk; 3, Grey Chalk or Chalk Marl.

These have been in undisputed use for very many years, not because they do not require any modification to render the accordance more definite and more rigidly corresponding to the accumulation of information which has been going on since their introduction, but chiefly because chalk,—at least English chalk,—is white or of a pale grey, which when the beds are in a dry state is so nearly white, that ordinary eyes do not see the difference, and ordinary collectors do not care about it so long as they can get hold of a fine fossil.

Still, however, it is very necessary, and high time that some one should take in hand to define accurately the lines of division, especially that between the upper and lower white chalks.

I doubt very much that the cessation of the bands of flints denotes the demarcation between the upper and lower white chalk (middle chalk of some authors): they should be properly, and must be ultimately, separated by a characteristic difference in the distinguishing organic remains.

With the lowermost bands of flints (Plate II. a) very numerous beds of ventriculites and sponges set in, and are continued far below the termination of the layers of flints, down to a very thick bed of pure white chalk (b), that rests upon a very marked and peculiar stratum about two feet thick (c), which, from the weathering out of its upper and under surfaces, forms a marked line as far as the eye can see the distinctions of bedding all along the coast.

This bed, in my own note-books and in conversation, I have familiarly termed the "two-foot stratum."

Below this we have again a thick bed of white chalk, free from flints. At least, such is the order in the section to which these remarks more particularly refer, namely, that presented by the East or Castle Cliff at Dover, of which we give a view in Plate II.

This "two-foot stratum" is persistent throughout Kent, and I have met with it both in Surrey and Sussex, and it will therefore probably form one of the best and most unmistakable guides in inland quarries to those particular beds of white chalk to which we wish to draw attention, for the purpose of getting all the information we can as to their geographical area, order of succession, and organic contents in other chalk districts, so that the true horizon of division, as formed by distinctiveness of organic remains, may be properly made out.