before状语从句的问题

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.请教一下专家老师，红色部分的句子结构是否有问题啊？这是主句被简化了么？

红字部分为一个beginning目前分词短语和一个before时间状语从句，都是前面这个句子Then he began to read all round the subject. 的状语。beginning应小写，前面的句号改为逗号。