When The Librarians attempt to break the quartz glass by singing, Cassandra claims the note they all need to sing together is "two octaves above middle C". This note is out of most people's vocal range and in fact, Cassandra and Jacob are only singing one octave above middle C. Ezekiel is, surprisingly, the only one who hits the correct note, singing two octaves higher than middle C.
The coordinates for the location of the henge are given as 84.3 N, 18.5 E. This is in the Arctic Ocean north of the Svalbard archipelago; Niagara Falls is at 43.1 N, 79.0 W.
Jenkins claims he had to leave Nicole stranded in the past because everything she did was "prophesied" so it was vital she got around to doing it. This begs the question by whom it was prophesied that the keepers of all knowledge place so much stock by the convenient anonymous prophecy.