These are original works, which cover a broad range of materials. They can be:
1. Original research published
as journal articles,
2. Original theories, ideas etc.,
3. Diaries, memoirs, research notes, data sets etc.,
4. Surveys, questionnaires, and
5. E-mails and opinion polls.
For example: A caveman drew
a picture of a mammoth on the wall in his cave. A 21st Century scientist
stumbled upon the cave and discovered the picture. He then studied the
drawing and developed a theory to reconstruct the life of the caveman
who drew the picture thousands of years ago. He published his findings
in a professional journal. Both the original drawing and his paper are
considered as primary sources.