M. R. Fedotov's Чувашско-марийские языковые взаимосвязи is study of borrowings in Chuvash and Mari. There's some material about the historical context for this language contact. But then, because such borrowing went mainly in one direction, the bulk of the book concerns Chuvash loanwords in Mari. Like Räsänen's Die tschuwassischen Lehnwörter im Tscheremissischen, he characterizes the phonetic correspondences in Mari's Chuvash loanwords (and how we know they are from Chuvash and not Tatar), but Fedotov goes further by categorizing the loanwords into various semantic domains, and by listing suffixes that Mari has borrowed (or possibly borrowed) from Chuvash. Almost half of the book then consists of a list of Chuvash loanwords borrowed into Mari. There is however, no reverse index, so one cannot readily look up if a Mari word is a Chuvash loan.
Mirroring the lopside relationship between these two languages of the Middle Volga, only 40 pages out of 335 deal with what Chuvash has borrowed from Mari. Fedotov only spends a page categorizing them semantically, and the rest is a dictionary of Mari loanwords in Chuvash.
The only weakness in the book is that it is concerned solely with the borrowing of lexemes and affixes, and it does not deal with e.g. Mari's adoption of converb constructions or the similarities between the tense systems in modern Chuvash and Mari. However, Fedotov does exhaustively cite other studies, and the reader will have an idea of what pre-1990 publications he can look to for this. Чувашско-марийские языковые взаимосвязи is a relatively accessibly written and clearly structured work, and will be of great use to students of Mari and Chuvash from a historical linguistics perspective.