merging string [] in foreach loop

Question

string[] drives = Directory.GetLogicalDrives();

foreach (string d in drives)

{

string[] d1 = Directory.GetDirectories(d);

string[] pathlist = fde.Union(falaa).Union(d1).ToArray(); 

}

 

//fde is the nother path list 

//falaa is the nother path list  

* pathlist is the collection of all lists

 

in path list i am not able to store the list, i know very well it is a mistake in code?