@becoin I don't think that's correct. If you look at the 24 hour volume rankings page on CoinMarketCap it never reports BTC volume as anything other than buying and selling of BTC in all the different FIAT pairs. When ETH is bought and sold for BTC, that volume is exclusively reported as ETH volume. If what you're saying is true, then every time an ETH is bought or sold for BTC, the volume is attributed on both sides of the ledger (i.e. it's ETH volume and it's also BTC volume). That's not how it works. CoinMarketCap treats Bitcoin as the primary crypto currency and when Alts are bought and sold, their volume of sales are reported under their respective identities and that volume is not then also attributed to BTC's volume.

As I mentioned before, that's the current situation and if another crypto type were to end up with a greater market cap than BTC, CoinMarketCap will probably have to change the manner in which volume is calculated (and there'd be some complications with that when - if ETH was higher market cap - ETH/BTC buy/sells would have to be taken out of the measurement and only ETH/FIAT left in; as is the case currently with BTC).