134 ROYAL SOCIETY OF CANADA 
ian granite, that is, granite which forced its way upwards in a molten 
state from deep in the earth, filling gaps and areas of weakness caused 
by movements of the earth’s crust in the older Silurian rocks. Now, 
at this time, it is fairly certain, the St. Croix river did not exist, 
and the present river bed was filled with Silurian rocks; or, more 
correctly, the river bed had not yet been cut out of the rocks. On the 
present site of the island there was probably some gap, or fault-line, 
in the Silurian rocks, and into this the molten granite was forced 
from below, just as it was in many other isolated masses now forming 
hills in this region. Later, in the course of the ages, the St. Croix. 
river began to flow over this place, and gradually, by the slow but 
resistless process of erosion, aided by the presence of contact and fault- 
lines, cut down the rocks until the river bed reached the granitic mass 
now forming the island. After that it cut out the softer Silurian 
rocks around it much faster than it could cut the hard granite itself, 
so that finally the granitic mass was left as a hill rising from a plain 
of the softer rocks. Then the land sank, and the sea entered this valley 
to such a depth that the top of the hill only was left above the sur- 
face; and this is the probable origin of the rocky part of Dochet 
Island. 
The soil resting upon these rocks is of glacial origin. It is known 
to geologists that in the glacial period, some thirty or more thousands 
of years since, a sheet of ice several thousands of feet in thickness 
moved southeastward over this region. This ice smoothed these 
granite rocks, as may be seen beautifully at the north end of the 
island, and would have left them but naked rounded ledges had not 
the same ice sheet carried an abundance of soil ground from the rocks 
in its passage, which soil was deposited, especially as it melted, around 
and in the lee of the core of the island. The glacial movement on 
the island was almost exactly true southeast (a trifle east), as is clearly 
shown by the course of the glacial grooves on the north end of the 
island; this is why the great mass of the soil of the island lies on the | 
southeast side of the rocky axis in the form of a long point ending 
in an abrupt bluff (Fig. 5), precisely such a point as is found in similar 
situations near by at Sand Point, Oak Point, Navy Island and elsewhere. 
The fact that this soil is mostly fine, thus forming good agricultural 
land, indicates that its deposition took place in quiet water. Had the 
conditions been different, and a coarse boulder soil replaced it, Dochet 
Island might have had no history. Only a few boulders exist on and 
around the island. Those above the tide, notably the huge one to 
the northward of the lighthouse, were, of course, brought here by the 
glacial ice from far to the northward at the time the soil was laid 
down, which explains their composition out of rock different from that 
