1 66 
Mr. Weaver on the 
of small and minute rounded and angular grains of quartz, nu- 
merous minute scales of white mica, small fragments of clay slate, 
and sometimes portions of felspar, cemented by clay slate. The 
greywacke slate is a similar rock, with a slaty structure ; and it is 
the predominating rock through these hills. The rock at Wind- 
mill hill ranges 10° north of east and south of west, which is 
the general direction in these hills, but sometimes more toward the 
north-east and south-west, exhibiting also at times an undularly 
curved slaty disposition. The dip is toward the south-east, and 
generally at an angle of about 45®. 
The greywacke slate of Windmill hill is remarkable for contain- 
ing subordinate beds of granite. I have traced three very distinct 
beds, (one of them for more than forty fathoms in length) along 
its north-western brow, interstratified with the greywacke slate. 
The uppermost bed is between three and four fathoms, and each 
of the other two from two to three in thickness. They are re- 
spectively fifty or sixty yards apart, separated by greywacke slate ; 
and all these rocks dip 45° to 50° toward the south-east. * 
Some of these granite beds are to be traced to the westward near 
the turnpike road, opposite to Rusty hill. They consist of a small 
and fine grained intermixture of yellowish and greyish white fel- 
spar, greyish vitreous transparent quartz, and flakes or scales of 
mica, white and silvery, with some small scattered portions of a 
* The granite of this place has been termed by other observers a porphyritic felspar. 
It requires, however, only a close examination to discover the three constituents of 
granite In their usual state of combination. The grain, it is true, is sometimes so small, 
that the aid of the lens becomes necessary in order to detect its composition ; but if this 
were a solid objection, the granite at the northern foot of Cadeen, as well as that of many 
other quarters, might become subject to the loss of its title. Geology can scarcely advance 
in its career, unless it be generally agreed to deduce the names of rocks from their com- 
position and structure only ; without any regard to the relative position in which they may 
be found. I shall have occasion to re-advert to this observation in the sequel. 
