COLUMNAR STRUCTURE IN LIMESTONE. 37 
Mount Wissick section. Feet. 
E. Argillaceous limestone with corals and other 
fossils . 35 
D. Bluish grey sandstone with fossils 50 + 
C. Finely laminated blue limestone with columnar 
structure in lower two-thirds 1 40 + 
B. Red and green shale.. 18+ 
A. Green, shaly, fine textured sandstone probably in 
part of volcanic origin. Saucer-structure (mud- 
cracks) well developed 50+ 
The beds of columnar limestone occur, as will be seen from 
this section, in a series in which sandstone and shale deposition 
alternated with limestone deposition, each in turn prevailing 
long enough to build 20 to 50 feet of beds. The three lower 
divisions of these beds, including the columnar limestone, are 
very sparingly fossiliferous where not entirely barren. The 
lowest bed exhibits a striking example of a variety of sun- 
cracked beds in which the margins of the irregularly rounded 
plates have warped upward, giving them a saucer like appearance. 
Littoral conditions of deposition are thus indicated for the sandy 
shale 20 feet below the limestone under consideration. 
The limestone of bed “C” is a continuation or recurrence of 
the littoral conditions, indicated by the sandy shale, in the 
opinion of the writer. If viewed only from the surface of the 
strata, the columnar structure of the limestone is not evident, and 
the mud-crack origin of the polygonal figures appears clear. 
Columnar structure, however, is not ordinarily associated with 
mud-cracks and the reason for the association of the two which 
this interpretation indicates requires consideration. The factors 
believed to be responsible for this association of columnar 
structure and mud-cracks can be advantageously considered in 
the light of some observations made by the writer on mud- 
cracks on the shores of the Bay of Fundy. 
1 The columnar structure of this bed was first noted by Logan in 1863 (Geol. of 
Can. p. 421). It was again mentioned by Bailey and Mclnnes in the detailed section 
of Mount Wissick, published in 1889 (Geol. Surv. of Can., new ser., vol. Ill, pt. II, 
p. 31M. 
56815 — 3 * 
