before狀語從句的問題

The great theme was at Prescotts disposal. In order to feel sure-footed in the language, he went over his Spanish grammar again. Then he began to read all round the subject. Beginning with the general laws of nations, the constitutional history of England, the histories of the continental countries, France, Italy, Germany, Portugal, the general history of Spain, before he settled on his special field.請教一下專家老師，紅色部分的句子結(jié)構(gòu)是否有問題啊？這是主句被簡化了么？

紅字部分為一個beginning目前分詞短語和一個before時間狀語從句，都是前面這個句子Then he began to read all round the subject. 的狀語。beginning應小寫，前面的句號改為逗號。