How do stock price splits work?

I know when companies decide that the prices are too high, they split the stock thus reducing the prices. What I don't understand is how it works on the charts. For instance, in Oct 2013, Google's price went past 1200 or something. Then they split it 2 for 1 and became ~600. I don't know about last year, but they split a couple months ago again from 1200-1300 to ~600. So I thought all of the prices will be adjusted, but price price from 2013 is shown as ~600, not ~300. I don't understand how the charts adjust the prices. Because if the price starts from 600 after the split in 2013, and risen to 1300 in 2015, and then there's a split, the price from 2013 should be shown as 300? Or there's something I missed