In this pattern an infinitive phrase is to be added with the proper word order for the intended result (to infinitive).This is what you Mr.White, means by reverting to the original sense,or one of the original sense, of the sentence .Volcanic rock-----s,main cl.were carved------v (passive)(to be) using simple tools-------when (to be) added for the complete sense is an abbreviated infinitive phrase, a dangling participle phrase qualifying main clause, object of the verb(=were carved).Reverting to the original sense,Mr Black,:-'using the simple tools' is participle phrase which is changed to passive voice by the (doer)eg:-Simple tools were used(by doer)to carve from rock.

This sentence has two action verbs (transitive) carried out by the same doer of actions (subject of the sentence).1. [the doer] generally carved 'them' (object of carve) from volcanic rock2. [the doer] used simple tools (object of use)分詞構句:  Using simple tools, [the doer] generally carved 'them' from volcanic rock.把'carve'變成被動語態: They were generally carved from volcanic rock using simple tools.因為'use'這動詞是帶著一個目的去'do'(不動式-to carve)另一件事, 所以原句可以是:[其中一種寫法]  Simple tools were used to generally carve them from volcanic rock.[主動式]  The artists used simple tools to generally carve them from volcanic rock.當然, 亦可以簡化一點, 用介詞取代分詞'using':They were generally carved from volcanic rock with simple tools.

They were generally carved from volcanic rock ,using simple tools.因為 rock 不可能是using simple tool的邏輯主詞，所以 using simple tools分詞片語当副詞修飾其前主要子句較符合文法規則或They were generally carved from volcanic rock by using simple tools.亦可

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