Correspondence — Mr, Charles Moore. 343 



place unless the area is depressed beneath the sea, and that marine 

 denudation will obliterate all trace of such faults at the surface. 

 But surely if we are to call in wide areas of upheaval, we cannot 

 limit the effects to a marine area any more than we could to a 

 terrestrial area. No doubt at the present day there would be just so 

 much the greater chance of a marine area being raised, as 

 extensive oceans preponderate over extensive continents. Certain 

 great faults have left their impress on the configuration of the 

 country, and if that impress is modified, it is sometimes as much by 

 subaerial as marine denudation. The Bala fault might be quoted 

 as an example. Ed. Wilson. 



Nottingham, June. 1868. 



ON THE DEVELOPMENT OF THE LOOP IN THE TEREBPATULIDiE. 



Sir, — In your last number, Mr. C. J. A. Meyer, in a paper on 

 Cretaceous Brachiopoda, offers some observations on the loop of 

 Waldheimia, Terehratula, Terebratella, etc. 



I do not wish to enter into a discussion on the desirability of 

 separating the two former generically, the greater or lesser extension 

 of the loop being their only distinction, but simply to say that the 

 correctness of the figures given in my paper on '' The Development 

 of the Loop in Terehratella,'' Geologist, vol. iii., pi. xii., figs. 1-4, does 

 not admit of a moment's doubt. They are not, as suggested by Mr. 

 Meyer, very minute ; and as, in the examples figured, the loops are 

 entirely free from the matrix, they can be studied with the greatest 

 advantage. The original sketches of the loops having been carefully 

 drawn by Mr. Davidson will be a sufficient guarantee that they are 

 correct. 



However difficult may be the question of a change in the calcified 

 interiors of some of the Brachiopoda, it is quite certain that with the 

 Terebratella Buchmanii we have a series of shells, none of which can 

 be separated by their external conditions, but which have notwith- 

 standing different forms of loops ; and it will be necessary either to 

 accept the suggestion that they are different stages of growth, or else 

 to create separate generic designations for shells that cannot by their 

 outer forms even be distinguished specifically. There is little doubt 

 that had they been obtained singly from different formations the 

 former would most probably have happened. 



It may interest some of your readers to know that I have just 

 found the genus TJiecidium in one of the lead veins of the Carboni- 

 ferous Limestone of Yorkshire, it not having been met with hitherto 

 in England below the Lias, or on the continent below the St. Cassian 

 Beds. The precise age of the vein yielding it will yet have to be 

 determined. Charles Moore. 



Eath, Jwte 18, 1868. 



DENUDATION NOW IN PROGRESS. 

 Sir, — In the very interesting and able article in your last number, 

 " On Denudation now in Progress," by Mr. Geikie, he has omitted to 

 take into consideration some circumstances of a restorative character 



