tentimes loud strokes, and ringing sounds

oftentimes > frequently

9 From under that deep rock most horribly rebound.

303.10

The cause some say is this: A litle while
2 Before that _Merlin_ dyde, he did intend,
A brasen wall in compas to compile
4 About _Cairmardin_, and did it commend
Vnto these Sprights, to bring to perfect end.
6 During which worke the Ladie of the Lake,
Whom long he lou'd, for him in hast did send,
8 Who thereby forst his workemen to forsake,
Them bound till his returne, their labour not to slake.

1 The cause, some say, is this: a little while
2 Before Merlin died, he did intend
3 A brazen wall in compass to compile

in compass to compile > to build in a circle

4 About Caer-merdin, and did it commend

it > [the project]
commend > entrust, commit

5 To these sprites to bring to perfect end.
6 During which work the Lady of the Lake
7 (Whom long he loved) for him in haste did send,
8 Who, thereby forced his workmen to forsake,
9 Them bound, till his return, their labour not to slake.

slake > abate, slacken

303.11

In the meane time through that false Ladies traine,
2 He was surprisd, and buried vnder beare,
Ne euer to his worke returnd againe:
4 Nath'lesse those feends may not their worke forbeare,
So greatly his commaundement they feare,
6 But there doe toyle and trauell day and night,
Vntill that brasen wall they vp doe reare:
8 For _Merlin_ had in Magicke more insight,
Then euer him before or after liuing wight.

1 In the mean time, through that false lady's train,

train > treachery, deceit

2 He was surprised, and buried under bier,

surprised > captured unexpectedly, ensnared
under bier > under a bier [underground, in a tomb]; _or:_ in a
sepulchre ("bier" sometimes taking this meaning by transference)

3 Nor ever to his work returned again:
4 Natheless those fiends may not their work forbear,

Natheless > Nevertheless

5 So greatly his commandment they fear,

commandment > authority; control

6 But there do toil and travail day and night,
7 Until that brazen wall they up do rear:
8 For Merlin had in magic more insight,
9 Than ever him before or after living wight.

wight > man, person

303.12

For he by words could call out of the sky
2 Both Sunne and Moone, and make them him obay:
The land to sea, and sea to maineland dry