I don't know if it's possible on Coinmarketcap, but I've found another website which allows you to get a csv file for the historic marketcap data.
Here you go:
https://data.bitcoinity.org/markets/market_cap/30d/USD?t=l
Here you go:
https://data.bitcoinity.org/markets/market_cap/30d/USD?t=l
That is a nice one for Bitcoin, thnx for sharing
Bitcoin is only one part of what I want to analyze, I am looking for data on the whole cryptocurrency market, so including as much altcoins as possible.