An insight on unit research: you need to know what other units served with your ancestor's unit. With a little information about the parent brigade, you can fill in gaps or add detail. Along those lines, you may also check for sources on the brigade commander(s).

In this case, Ferguson's Cavalry Brigade included the 2nd and 56th Alabama, plus the 9th and 10th Mississippi Cavalry and the 12th Mississippi Cavalry Battn. There's much more than most people really want just by opening the scope.

Here are a few web references which appear in a search for Ferguson's Cavalry Brigade:

http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=10038

http://civilwartalk.com/threads/brigadier-general-samuel-wragg-ferguson.19352/

http://www.ranger95.com/civil_war/generals_confederacy/samuel_wragg_ferguson.htm

https://books.google.com/books?id=wMoGAQAAIAAJ&pg=PA808&lpg=PA808&dq=Ferguson%27s+Cavalry+Brigade+1864&source=bl&ots=uQxxGq63OW&sig=w60WdUtbQXC3otd0zbqdmgXOfbY&hl=en&sa=X&ved=0ahUKEwilj4rhpvPJAhVL32MKHehbBuw4ChDoAQgkMAI#v=onepage&q=Ferguson's%20Cavalry%20Brigade%201864&f=false

Interesting post-war letter by a captain from the 2nd Alabama Cavalry who accuses Ferguson of executing Federal prisoners during the Atlanta Campaign (click on the letter image to open):
http://digital.archives.alabama.gov/cdm/singleitem/collection/voices/id/1947/rec/10