36 
MUSEUM BULLETIN NO. 2, 
numerous, thin, paper-like lines of sedimentation — thin laminae 
of argillaceous limestone alternating with less argillaceous 
bands; the limestone splits up freely on weathering into columns 
at right angles to the bedding, but it displays very little tendency 
to split along the bedding planes. „ A large number of these 
detached columns of limestone, with a length of from 10 inches to 
24 inches, are scattered along the front of the ledge. A very 
thin sheet of dark argillaceous and carbonaceous matter, usually 
about one-fourth of an inch thick, separates the faces of ad- 
jacent columns. An approximate estimate by Mr. R. A. A. 
Johnston places the carbon in this material at about 3 per cent. 
This thin, black film is essentially free from lime, affording no 
reaction with hydrochloric acid, although the faces of the columns 
adjacent to it effervesce vigorously with acid. The laminae of 
the limestone do not pass through this thin wall but stop abruptly 
on either side of it. The presence of this dark argillaceous 
partition between the faces of adjacent columns is a feature 
which distinguishes this structure from that characterizing the 
columnar structure of basalt. It distinguishes it also from 
joint structure, thus indicating an origin independent of the 
agencies which produce either joint or basaltic columnar struct- 
ure. The bed of columnar limestone occurs in a region where 
orogenic agencies have acted vigorously. The horizontal 
stresses developed by these agencies have resulted locally in 
shortening one diameter of the columns and in changing the 
original vertical relations of these to the bedding by several 
degrees. The effects of deformation are indicated by the 
inclination and slight flattening of the columns shown in Plate 
II. In most specimens observed the columns are vertical to the 
bedding. 
The structure described and illustrated by Plate II and 
Plate III, fig. 1, occurs in the lower two-thirds of a bed of 
limestone at the base of Mount Wissick on the shore of Temis- 
couata lake opposite Cabano, Quebec. The stratigraphic 
relations of this limestone are indicated in the following section 
which represents only a small portion of the Mount Wissick sec- 
tion. 
