HILL: GEOLOGY OF JAMAICA. 79 
as the Cobre formation. The slopes are usually covered with dense vege- 
tation, good rock exposures not being plentiful except in the immediate 
Stream way, Even then they are encrusted with tufaceous material, so 
that their structure and arrangement are largely concealed. The follow- 
ing extract from the notes of our traverse of this canyon will give an 
idea of the composition and structure of these beds, Miles read north 
from Spanishtown. 
0-44 miles! — The river flows in a V-shaped alluvial plain indenting 
the canyon to this point. 
41 miles. — A road metal quarry reveals the texture of the white lime- 
Stone, which is here composed almost entirely of small angular lumps of 
firm limestone, chalky white in color, associated with a matrix of very 
fine pulverulent chalky sinter, free from clay, but commonly termed 
" White Marl," as are all other soft formations. There are also a few 
Small lumps of compact gray or dove colored limestone (dolomite ?). 
This formation is of cavernous or “honeycombed ” texture and weathers 
Into irregularly crystalline limestone, constituting ragged karrenfelder on 
orizontal surfaces. Furthermore, the faces of the bluffs are in places 
“oated with self-derived tufa, and are so indurated that these outerops 
have a massive non-stratified appearance. This limestone differs from 
that of the ‚ambridge and Montpelier beds in the entire absence of 
lamination or traceable lines of bedding. 
43-8} miles. — The limestone is continuously exposed in the vertical 
bluffs through which the river cuts its way. No trace of bedding can 
Anywhere be made out, and the surfaces of the cliffs are everywhere 
Very indurated. 
8 miles. — The inclination of the beds, hitherto indeterminate, shows 
ù strong south dip. 
83-9 miles. — The vertical cliffs show dips to south of 30° (estimated), 
tho anglo increasing in steepness as we go north. While these exposures 
Me moro massive looking than those before noted, quarries reveal the 
‘amo texture as that noted ht Mile Post 41. 
9-11 miles. Bog Walk Village. — Here the canyon ceases, and the 
Ountry opens out into the interior valley of St. Thomas-in-the-Vale. 
Süperb exposures of the Cobre limestone and its basal conditions are 
"own in the bluffs at the upper end of the canyon, as illustrated in 
“gure 25. 
Tho pebble and buff-colored marls grade into the limestone, and repre- 
"ent, its initiatory littoral. A few poor and indeterminate casts of fossil 
1 From Spanishtown. 
