Sentence:  The transition from "Birc"("h")"-" to "Birt-" is obscured by the <WSD>palæography</WSD> of "-t"("h")"-", "-c"("h")"-", undistinguishable<!-- hyphenated as “un-distinguishable” in the source text --> in many sources. 
Meaning of the word marked with <WSD> tags:  (paleography) (study of ancient forms of writing).