That > [So that]
6 High growing on the top of rocky cliff, 7 Whose heartstrings with keen steel nigh hewed be,
heartstrings > {Tendons or nerves supporting the heart; hence, here: central fibres of heartwood} keen > sharp
8 The mighty trunk half rent, with ragged rift
rent > split, torn ragged rift > ragged fissure ("ragged" also = "discordant", "harsh" (e.g. at 112.23:4); "rift" may also mean "rubble": cf. this same phrase at 212.4:5)
9 Does roll adown the rocks, and fall with fearful drift.
adown > down drift > motion, momentum (cf. Aen. 2.626-631)
108.23
Or as a Castle reared high and round,
2 By subtile engins and malitious slight
Is vndermined from the lowest ground,
4 And her foundation forst, and feebled quight,
At last downe falles, and with her heaped hight
6 Her hastie ruine does more heauie make,
And yields it selfe vnto the victours might;
8 Such was this Gyaunts fall, that seemd to shake
The stedfast globe of earth, as it for feare did quake.
1 Or as a castle, reared high and round, 2 By subtile engines and malicious sleight