76 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
that time, after the manner of granite just intruded. The Lower 
Carboniferous rocks afterwards deposited among the Devonian ridges 
in the east were, in tbeir turn, folded, and they too compose a sub- 
ordinate part of the plateau. 
Form. — But all this constructional topography due to folding has 
been changed (Plates 1 and 2). The geologist now directs his exploring 
canoe over a thousand square miles of granite moulded in the low re- 
lief of gently undulating hills separated by shallow lakes. He finds but 
little trace of the mountain-cover which blanketed the intrusions and 
permitted the slow crystallization of the vast igneous bodies. As little 
does he anywhere find the original surface of the ranges. There remain 
to him only the edges of slate or quartzite band, that once, to right, 
stretched up over the roof of a now vanished arch, and, to left, formed 
half of a rained trough, which he can stiil decipher, though tattered 
and corrugated on its rims, the roots of an all but completely destroyed 
mountain mass. Throughout these fifteen thousand square miles, the 
observer finds no hill more than one thousand feet high, and ninety 
per cent of the plateau is less than six hundred feet in altitude above 
the sea. It will be well to note some of the readings of elevation which 
I have compiled from the various sources already mentioned ; many of 
them are merely barometric determinations, but no serious error is 
believed to result from their use. 
In addition to the fact that the coastal elevations are low, it was 
speedily observed that they are systematically related. At the mouth of 
St. Mary’s Bay, the bed-rock surface of the hill-tops stands at from one 
hundred and fifty to two hundred feet above the sea. Thence a more 
rapid rise northeastwardly brings the average summit southeast of Digby 
to the five-hundred-foot contour, and the long escarpment of ‘ South 
Mountain,” running north-east by east, remains at that elevation for 
some sixty-five miles. Along the roughly parallel line of the Atlantic 
coast, the heights vary from seventy feet at Cape Sable to one hundred 
and fifty feet at Halifax. Profile sections taken transverse to these two 
belts of elevation show that there is a fairly gradual descent from one 
to the other, in a southeast by south direction, a descent interrupted 
only by local and faint reliefs to which reference will presently be made. 
It will be further noticed that the greater height of the hills near Hali- 
fax is related to a corresponding proximity of the Atlantic shore to 
‘South Mountain,” proving an essentially equivalent angle of slope for 
the surface throughout the western half of the plateau as far as the 
town of Digby. The same angle and direction of slope characterizes 
