Tarr — Origin of the Chert in the biirlington Limestone. 423 



fossils just the same as the other liinestone does. The cracks run 

 in all directions through the nodules. Usually they are found 

 on the upper surface but they may occur also on the lower. 

 They are most abundant in the thicker portions of the nodules. 

 The interesting structural feature, stylolite, is wonderfully well 

 developed in the Burlington limestone. Very frequently the 

 plane of the stylolites may follow a plane of chert nodules (see 

 fig. 5, (I). When such is the case the outside of the nodules 



Fig. 8. 



Fig. 8. Chert nodule containing cracks filled with limestone. About one- 

 third size. 



shows the striated faces which are produced by the stylolites. 

 Planes of stylolites have been observed passing through the 

 limestone immediately over the cracks in the chert nodules 

 and showing no evidence of deviation from a plane. This in- 

 dicates that the cracks in the nodule were filled before the 

 development of the stylolites. It is not thought, however, that 

 the development of these cracks was due entirely to the flat- 

 tening process, but that they were partly developed during the 

 changes which the silica underwent in the early stages of the 

 development of the nodule, especially during the change due 

 to the loss of water. 



