It may half been

"It may have been . . .": Answering the question "What broke the camel's back?" -- that is, what was the cause of Tim Finnegan's fall from his ladder, and what caused the Temple to fall or the Tower of Babble to collapse (coming after a long section about Finnegan's role as a builder of great structures). The camel is featured in the previous two setences, referring to Crop-eared, Mohammed's camel.

The full sentence reads:

It may half been a missfired brick, as some say, or it mought have been due to a collupsus of his back promises, as others looked at it.