Complex sentence: In line with his group's ethnic custom, the unknown builder built the cabin with logs raised vertically, rather than horizontally as had already become the custom among English-speakeing frontiersmen farther east.
Split into simpler sentences: In line with his group's customary architecture, the unknown builder built the cabin with logs raised vertically. This was different than the logs placed horizontally, as had become the custom among English-speaking frontiersmen farther east.