Sentence:  ... if those Persons who are curious in "collecting" either "Minerals", or the "Shells", "Teeth", or other Parts of Animal Bodies that have been buried in the Earth, do but search the "Hills" after "Rains", and the "Sea-Shores" after "Storms", I dare <WSD>undertake</WSD> they will not lose their Labour. 
Meaning of the word marked with <WSD> tags:  To pledge; to assert, assure; to dare say.