Is using Stacks (the data collection class) allowed in Silverlight? I have used Stacks in my WPF c#...

Is using Stacks (the data collection class) allowed in Silverlight?  I have used Stacks in my WPF c# application.  But Visual Studio complains when I declare a Stack in my Silverlight APP.  I need to use this class.  Is there a substitute?

I tried searching but the results from search engines talked about stack panels, which are not the same thing.