GEOLOGY AND MINERALOGY. 305 
their outerop and the upper termination of the Hudson River Group, the Medina 
Sandstone should be found. It is, nevertheless, impossible to determine this in a 
satisfactory manner, and consequently to ascertain the exact thickness of the 
Hudson River Group, as the intermediate space is so greatly obscured by drift 
and vegetation. 
5. The beds of siliceous limestone on the top of the Mountain are polished and. 
striated by glacial action. The polished surface of the stone exhibits two sets of 
strie or furrows, crossing at a slight angle, but having a general N.N.W. andS.S.E. 
direction. Here and there, the lines of furrow pass across projecting hard points, 
under the south side, or lea, of which, a slight interruption in the furrow takes 
place. This shows the abrading agency to have moved from the north, south-. 
wards, 
6. On passing over the summit of the mountain, towards the south-west and 
west, limestone strata, containing Niagara fossils, crop out; but, as these extend 
beyond the limits of the Blue Mountain district, they were not specially examined, 
7. The slopes of the Mountain and the surrounding country are more or less 
thickly covered by drift-clay and boulders. At the foot of the Mountain, on the 
south-east side, a high ridge of drift extends for some miles in a direction roughly 
parallel to the escarpment. This ridge has at first sight a certain resemblance to 
the terminal moraine of an ancient glacier; but it is evidently nothing more than 
a sub-aqueous formation or fringing bank, accumulated during the drift period, 
when the summit of the mountain formed a broad shoal, or low island, in the 
glacial sea. The formation of the escarpment itself is due to the denuding forces 
of a still earlier time; and the enormous amount of sedimentary matter carried 
off during its denudation, may to some extent be realized, when we consider its 
height above the general level of the country, and its extension to the south of 
Lake Ontario. 
PROFESSOR DAWSON, LL.D., ETC.,, ON VEGETABLE STRUCTURES IN COAL. 
The February number of the Journal of the Geological Society contains, amongst 
other valuable papers, a communication of no ordinary interest, by Dr. Dawson 
of McGill College, Montreal, on the characters of the different vegetable structures 
preserved in coal. The paper is illustrated by a great number of lithographed 
figures, without the aid of which, it would be useless to attempt anything like a 
special analysis of its contents. The structures preserved in the soft fibrous lay- 
ers called “mineral charcoal,” are first investigated; and afterwards, those 
preserved in the compact or lustrous portion of ordinary coal. Many new and 
exceedingly interesting details are brought out by these investigations, rendering 
Dr. Dawson’s paper one of the most valuable contributions to our knowledge of the 
Carboniferous flora, that has appeared for some time. The paper concludes with 
a few general deductions, as given in the following extract :— 
1. With respect to the plants which have contributed the vegetable matter of 
the coal, these are principally the Sigi//arie and Calamitew, but especially the 
former. With these, however, are intermixed remains of most of the other plants 
of the period, contributing, though in an inferior degree, to the accumulation of 
