Recovered from Prosper Bluff.
"A worn book hand-written in the traditional Ura script.
Amid the scrawled notes, the book contains various indecipherable scientific diagrams, drawings, and mathematical formulae."
- "So many secrets in there and she can't even read it. Her father's own journal."
To Rucks: "Can you read any of this? Do these charts and formulas mean anything to you?"
- "If only I'd known half the secrets o' the Calamity were tucked away in that book...I'd have worked to translate it right away."
To Zulf: "What do you make of these drawings and diagrams? Isn't this written in your native language?"
- "The scientific journal written in Zulf's native tongue. He learned so much from it. Too much."
The Hidebound Journal was written by Zia's father, Venn, a brilliant Ura Mancer. While Venn worked voluntarily at some point, it is clear he disapproved of the Mancers' work as he refused to discuss any aspects of his job with Zia. He is coerced into returning to work after his daughter is framed for treason against the City.
Venn's journal reveals that the Calamity was the result of a Mancer project that would eradicate the Ura by sealing the Tazal Terminals. Because Venn was employed in the creation of this device, he secretly sabotaged the project to turn its destructive power against the Caelondians.
It is implied that Venn was also forced to deploy the device. He would therefore be directly responsible for the Calamity.
The Journal is concrete proof that the Calamity was, in fact, attempted genocide. Zulf, who is the only character literate in the Ura language, is infuriated by this knowledge. He attempts to destroy the Monument before leaving the Bastion, promising Rucks he will succeed where the Calamity failed.