Ugh. I had this all typed out and hit the wrong button. I'll try to do it again....

K, so, when glaciers melt, they shit out a bunch of sediments. If this stuff is just deposited directly where the glacier was (stagnation), it's called till. If this material is carried by water coming off the glacier, it's called glaciofluvial (GLFL). If it's carried by water, it gets sorted somewhat, with heavier chunks settling out first, then sands, then ultimately clays, but encountering clay GLFL is pretty uncommon.

what are the horizons?

From left to right:

LFH - Dead leaves, sticks, mosses, organic matter Ae - the first horizon to develop on the GLFL deposit, and the first encountered. the 'e' indicates that something has leached from it. In this case, it's iron. in other cases it can be labile humic acids or clays. The leaching process is called eluviation.
Bm - This layer is the last one developed, and develops overtop of the C and between the A through pedogenic action, like eluviation. Sidebar; when something is being deposited into a horizon in question, it's called illuviation. in this case, the illuviation wasn't strong enough to change the classification of the soil so it gets to the 'm' modifer, for 'minor development'
C - this is the last horizon and the most like the the GLFL parent material. No modifiers here, since there's no mottling, illuviation, or carbonates associated with it.