889 
of Edinhurgh, Session 1883-84. 
the surface of the boulder or the rock, become blunted under severe 
pressure, and be at length crushed to pieces. 
In the Tynecastle boulder, strise were seen on both the upper and 
the under surface. Those on the upper surface showed incision 
from a ivesterly point j those on the under surface, showed incision 
from an easterly point, judging by the test before referred to. If 
the boulder had been pushed over sharp rocks from the westward, 
the ruts on the lower surface would, according to that test, show 
that they had begun to be formed at the east end. After the 
boulder had become fixed in position, a drift of hard shingle pass- 
ing over the top from the west would produce striae beginning at 
the west end. 
It is evident that striae could be formed less easily on the vertical 
or lateral sides of a boulder than on the upper or under sides, as 
the incising pebbles might not, in the first casej so easily continue to 
move in a horizontal direction. One boulder is mentioned where 
striae were seen on both sides of the boulder — these sides meet- 
ing at, and radiating from, a point at one end, as shown in the 
woodcut on p. 802 of Abstract. The case is interesting on account 
of its bearing on the agency which produced the striae, as it must 
have been such as to be capable of being separated into two 
currents when it reached the boulder, in which case a current 
would flow along each side, pushing and pressing drift on the 
surface of the boulder as it passed. 
It is proper also to notice, as bearing on the same question, that 
boulders sometimes show two sets of striae, the one set crossing the 
other obliquely, indicating a change in the direction of the striating 
agent, or else in the position of the boulder. The case, for example, 
on page 844 of Abstract^ shows one set of striae running N.H.W., 
and the other W. by S. (Easter Duddingstone). 
As the study of striations may throw light on the nature of the 
transporting agent, it is right to take notice of striations on solid 
rocks \ for if there are on them two sets of striations crossing one 
another, the cause must be ascribed either to a change of direction 
in the movement of the striating agent, or to the advent of another 
striating agent from a different quarter. 
Examples of two sets of strioe on a rock surface will be seen in 
Abstract, p. 839 {Glasgoio) and p. 849 {Garden Hill), 
