*Conversations on Geology: Comprising a Familiar Explanation of the Huttonian and Wernerian Systems: the Mosaic Geology. G Penn - 1828.[https://books.google.com/books?hl=en&lr=&id=eTNRE9A319UC&oi=fnd&pg=PR24&dq=granville+penn&ots=uu3RW9SniA&sig=cnCundmHjaKnRezQotbF3Sa9I40#v=onepage&q=granville%20penn&f=false] | *Conversations on Geology: Comprising a Familiar Explanation of the Huttonian and Wernerian Systems: the Mosaic Geology. G Penn - 1828.[https://books.google.com/books?hl=en&lr=&id=eTNRE9A319UC&oi=fnd&pg=PR24&dq=granville+penn&ots=uu3RW9SniA&sig=cnCundmHjaKnRezQotbF3Sa9I40#v=onepage&q=granville%20penn&f=false] |