Thank you, all of you, for helping me to get out of this. For those who
want to do the same thing here is the code i have made to get the type
of the excel data field :

Public Function GetDataFromXL() As DataTable
Dim dt As New DataTable
Dim dr As DataRow
Dim plage As Excel.Range
Dim col As Integer
Dim row As Integer

plage = XLApplication.Selection()
col = plage.Columns.Count()
row = plage.Rows.Count

'Dim ii As String = XLworksheet.Type.GetTypeCode.ToString

For i As Integer = 0 To col - 1
dt.Columns.Add("Col" & i)
Next

For i As Integer = 0 To row - 1
dr = dt.NewRow
For j As Integer = 0 To col - 1
dr(j) = plage.Value2(i + 1, j + 1)
Debug.WriteLine(VarType(plage(i + 1, j + 1).Value()))
Debug.WriteLine(plage.Value2(i + 1, j + 1))
Next
dt.Rows.Add(dr)
Next
Return dt
End Function

Hope this will help someone else.

Best Regards,