list.SkipWhile(t => !(t is Element)).TakeWhile(x => x is Element);

public static class EnumerableExtensions
{
	public static IEnumerable<IEnumerable<T>> GetPartitions<T>(this IEnumerable<T> source, Predicate<T> predicate)
	{
		var resultList = new List<List<T>>();
		List<T> innerList = null;

		foreach (var itm in source)
		{
			if (predicate(itm))
			{
				if (innerList == null)
				{
					innerList = new List<T>();
					resultList.Add(innerList);
				}

				innerList.Add(itm);
			}
			else if (innerList != null)
				innerList = null;
		}

		return resultList;
	}
}

public class BaseElement
{}

public class Element : BaseElement
{}

// Verwendung:
var list = new List<BaseElement>();
list.Add(new BaseElement());
list.Add(new BaseElement());
list.Add(new Element());
list.Add(new BaseElement());
list.Add(new BaseElement());
list.Add(new Element());
list.Add(new Element());
list.Add(new BaseElement());
list.Add(new Element());

var elements = list.GetPartitions(f => f is Element);