How is laserdisc information physically stored on the disc? I know that Laserdiscs store video in an analog composite format.

I also know that CDs and DVDs store audio data as a digitally-encoded bitstream with the bits stored as pits and islands in the disc surface, which is simply read by the laser.

How is the analog data physically stored on the laserdisc surface? If it's pits-and-islands, then the data is surely digital and not really "analog", but if it's analog then it must be some kind of surface that has a continuous "reflectivity" which can store multiple channels of data (composite video in some kind of carrier and audio channels) in a single stream, how is this possible? Stereo vinyl discs store stereo information in different dimensions, but you can't do that with a reflective surface.
Just about everything you'd like to know about LaserVision disks can be found in this Wikipedia page, including the details of how the composite analog video is stored in a series of pits and lands. 

Of course it's not strictly analog because it's sampled and later re-integrated, but there is no digitization of the video as we think of it today with Blu-Ray etc.