On further examination of the locality we discovered that the proximate cause of our escape was owing to the position of the rock near a piece of water, the extent of which we perceived when the fire in our neighbourhood had burned itself out. (A Voyage round the World by W.H.G. Kingston）注：岩山にいた主人公たちが野火から逃げ延びた際の事情についての記述です。
動画の後半部分でリスニング用音声が流れます。
英文を前から読んでいくために、語句のかたまりを作ります。こんな具合に課題文をスラッシュ（斜め線）で区切ります（スラッシュリーディング）。語句のかたまりを意識すると、リスニングで英語の意味をつかむのが楽になります。
On further examination of the locality／（主語が文頭にないときの主語の前）we discovered／（接続詞の前）that the proximate cause of our escape was owing to the position of the rock near a piece of water,／（コンマの後）the extent of which we perceived／（接続詞の前）when the fire in our neighbourhood had burned itself out.
語句のかたまりを前から訳していきます。
On further examination of the locality
周囲をさらに調べたところ
we discovered
私たちは気づいた
that the proximate cause of our escape was owing to the position of the rock near a piece of water,
私たちが脱出できた直接的な理由は岩山が水辺の近くにあったことだった
the extent of which we perceived
私たちはその水域の広さに気づいた
when the fire in our neighbourhood had burned itself out.
周囲の火が燃え尽きたとき
On further examination of the locality we discovered that the proximate cause of our escape was owing to the position of the rock near a piece of water, the extent of which we perceived when the fire in our neighbourhood had burned itself out.
On further examination of the locality→ on = 〜のすぐ後に、〜と同時に
owing to the position of〜→ owing to〜 = 〜のために、〜が原因で
周囲をさらに調べたところ、私たちが脱出できた直接的な理由は岩山が水辺の近くにあったことだとわかった。あたりの火が燃え尽きたとき、私たちはその水域の広さに気づいた。
今回の課題文では、関係代名詞の部分が訳しにくくなっています。意味のとり方のコツをご紹介します。
the extent of which we perceived when the fire in our neighbourhood had burned itself out→ the extent of which を本来の目的語の位置に戻します→ we perceived the extent of which when the fire〜→ which に先行詞を代入します→ we perceived the extent of a piece of water when the fire〜→「火が〜のとき、私たちはその水域の広さに気づいた」
