Index: /issm/trunk-jpl/src/m/classes/materials.py
===================================================================
--- /issm/trunk-jpl/src/m/classes/materials.py	(revision 24750)
+++ /issm/trunk-jpl/src/m/classes/materials.py	(revision 24751)
@@ -19,5 +19,7 @@
             intnat[i] = 4
         elif strnat[i] == 'litho':
-            intnat[i] = 5
+            intnat[i] = 6
+        elif strnat[i] == 'hydro':
+            intnat[i] = 7
         else:
             raise RuntimeError("materials constructor error message: nature of the material not supported yet! (''ice'' or ''litho'')")