202 



0. Holtedahl — Structures like Walcott^s 



been formed primarily, on the sea-bottom, but secondarily, 

 through alterations in the rock. 



Sedgwick holds that the particles of the rock, ^' after 

 deposition, seem to have undergone great internal move- 

 ments, — to have run into lumps and masses more or less 

 crystalline," etc. And he states concerning some plates 

 of the rocks which assume a discoidal form ^^and at first 

 sight might be mistaken for large Nummulites^^ (cf. the 

 plate-like Neiiiandia frondosa, Walcott's plate 6, figures 

 1-3) : ''That these changes took place after the deposi- 



FiG. 8. — Above, one of the Fulwell quarry structures. Below, a laminated 

 fibrous crystalline aragonite. Both natural size. 



tion of the rock, is rendered probable by the additional 

 fact, that the laminations of the beds may be often 

 observed to pass (without any deviation) through the 

 various subordinate concretionary masses." Another 

 fact that indicates the secondary origin is that ''the same 

 bed which in one end of a quarry is homogeneous, in the 

 other is almost made of these singular concretions."^ It 

 is also evident that Abbott and Trechmami regard the 

 structures as secondary, and Woolacott states in 1919:^ 

 "As Sedgwick pointed out in 1835, the concretions were 

 formed after deposition, and I have shown that they must 

 have been mainly produced before the folding and dislo- 

 cation of the strata took place." Again he says : "The 



« op. cit, pp. 89, 95, 97. 

 « Op. cit., p. 463. 



