diff --git a/resources/public/css/states.css b/resources/public/css/states.css
index f3001ed..466c708 100644
--- a/resources/public/css/states.css
+++ b/resources/public/css/states.css
@@ -6,10 +6,22 @@ td.water {
  	background-color: blue;
 }
 
-td.pasture, td.grassland {
+td.pasture, td.grassland, td.meadow {
 	background-color: lime;
 }
 
+td.crop {
+	background-color: yellow;
+}
+
+td.camp, td.house, td.inn, td.market {
+	background-color: gray;
+}
+
+td.ploughland {
+	background-color: brown;
+}
+
 td.heath {
 	background-color: chartreuse;
 }
@@ -29,3 +41,12 @@ td.climax {
 td.fire {
  	background-color: orange;
 }
+
+td.error, td.plague {
+	background-color: red;
+}
+
+td.snow, td.ice {
+	background-color: white;
+}
+
diff --git a/resources/public/docs/mw-engine/uberdoc.html b/resources/public/docs/mw-engine/uberdoc.html
index a2c9acf..8ccbf4e 100644
--- a/resources/public/docs/mw-engine/uberdoc.html
+++ b/resources/public/docs/mw-engine/uberdoc.html
@@ -3033,8 +3033,7 @@ net.brehaut.ClojureTools = (function (SH) {
 </td><td class="codes"></td></tr><tr><td class="docs">
 </td><td class="codes"><pre class="brush: clojure">(ns mw-engine.core
   (:require [mw-engine.world :as world]
-        mw-engine.natural-rules
-        mw-engine.utils))</pre></td></tr><tr><td class="docs"><p>Every rule is a function of two arguments, a cell and a world. If the rule
+            mw-engine.utils))</pre></td></tr><tr><td class="docs"><p>Every rule is a function of two arguments, a cell and a world. If the rule
 fires, it returns a new cell, which should have the same values for :x and
 :y as the old cell. Anything else can be modified.</p>
 
diff --git a/resources/public/docs/mw-parser/uberdoc.html b/resources/public/docs/mw-parser/uberdoc.html
index 90e8d17..97ed787 100644
--- a/resources/public/docs/mw-parser/uberdoc.html
+++ b/resources/public/docs/mw-parser/uberdoc.html
@@ -3053,7 +3053,7 @@ objective is to parse rules out of a block of text from a textarea</p>
    function, and return the sequence of such functions.</p>
 </td><td class="codes"><pre class="brush: clojure">(defn compile-string
   [string]
-  (map #(compile-rule % true) (remove comment? (trim (split string #&quot;\n&quot;)))))</pre></td></tr><tr><td class="docs"><p>Compile each non-comment line of the file indicated by this <code>filename</code> into 
+  (map #(compile-rule % true) (remove comment? (split string #&quot;\n&quot;))))</pre></td></tr><tr><td class="docs"><p>Compile each non-comment line of the file indicated by this <code>filename</code> into 
    an executable anonymous function, and return the sequence of such functions.</p>
 </td><td class="codes"><pre class="brush: clojure">(defn compile-file 
   [filename]
@@ -3404,7 +3404,7 @@ front of the sequence of tokens it returns nil.</p>
       (use 'mw-engine.utils)
       (let [afn (eval (parse-rule rule-text))]
         (cond 
-          (and afn return-tuple?)(list afn rule-text)
+          (and afn return-tuple?)(list afn (trim rule-text))
           true afn))))
   ([rule-text]
     (compile-rule rule-text false)))</pre></td></tr><tr><td class="spacer docs">&nbsp;</td><td class="codes" /></tr></table><div class="footer">Generated by <a href="https://github.com/fogus/marginalia">Marginalia</a>.&nbsp;&nbsp;Syntax highlighting provided by Alex Gorbatchev's <a href="http://alexgorbatchev.com/SyntaxHighlighter/">SyntaxHighlighter</a></div><script type="text/javascript">SyntaxHighlighter.defaults['gutter'] = false;
diff --git a/resources/public/img/tiles/ice.png b/resources/public/img/tiles/ice.png
new file mode 100644
index 0000000..1349ef0
Binary files /dev/null and b/resources/public/img/tiles/ice.png differ
diff --git a/resources/rulesets/ecology.txt b/resources/rulesets/ecology.txt
new file mode 100644
index 0000000..e4686f0
--- /dev/null
+++ b/resources/rulesets/ecology.txt
@@ -0,0 +1,99 @@
+## Ruleset which attempts to model predator/prey ecology (not very well yet)
+
+## Vegetation rules
+;; rules which populate the world with plants
+
+;; Occasionally, passing birds plant tree seeds into grassland 
+
+if state is grassland then 1 chance in 10 state should be heath
+
+;; heath below the treeline grows gradually into forest, providing browsing pressure is not to high
+
+if state is heath and deer are fewer than 6 and altitude is less than 120 then state should be scrub 
+if state is scrub then 1 chance in 5 state should be forest
+
+;; Forest on fertile land at low altitude grows to climax
+
+if state is forest and fertility is more than 5 and altitude is less than 70 then state should be climax   
+    
+;; Climax forest occasionally catches fire (e.g. lightning strikes)
+
+if state is climax then 1 chance in 500 state should be fire
+
+;; Climax forest neighbouring fires is likely to catch fire
+if state is climax and some neighbours are fire then 1 chance in 3 state should be fire
+
+;; After fire we get waste
+
+if state is fire then state should be waste
+
+;; And after waste we get pioneer species; if there's a woodland seed
+;; source, it's going to be heath, otherwise grassland.
+
+if state is waste and some neighbours are scrub then state should be heath
+if state is waste and some neighbours are forest then state should be heath
+if state is waste and some neighbours are climax then state should be heath
+if state is waste then state should be grassland
+
+## Herbivore rules
+
+;; rules describing the impact of herbivores on the environment
+    
+;; if there are too many deer for the fertility of the area to sustain,
+;; some die or move on.
+;; if deer are more than fertility then deer should be fertility / 2
+
+;; deer arrive occasionally at the edge of the map.
+
+if x is 0 or y is 0 and deer are 0 then 1 chance in 50 deer should be 2 
+        
+;; deer gradually spread through the world by breeding or migrating.
+if fertility is more than 10 and deer is 0 and some neighbours have deer more than 2 then deer should be 2
+
+;; deer breed.
+
+if deer are more than 1 then deer should be deer * 2
+
+## Predator rules
+
+;; rules describing the impact of predator behaviour on the environment
+
+if deer are more than wolves then deer should be deer - wolves
+
+;; if there are not enough deer to sustain the population of wolves,
+;; some wolves die or move on.
+
+if wolves are more than deer then deer should be 0 and wolves should be deer + 0
+
+;; wolves arrive occasionally at the edge of the map.
+
+if x is 0 or y is 0 and wolves are 0 then 1 chance in 50 wolves should be 2 
+
+;; wolves gradually spread through the world by breeding or migrating.
+
+if state is not water and wolves is 0 and some neighbours have wolves more than 2 then 1 chance in 5 wolves should be 2
+
+;; wolves breed.
+
+if wolves are more than 1 then wolves should be wolves * 2
+
+## Potential blockers
+
+;; Forest increases soil fertility. 
+if state is in forest or climax then fertility should be fertility + 1
+
+
+## Initialisation rules
+
+;; Rules which deal with state 'new' will waste less time if they're near the
+;; end of the file
+
+;; below the waterline we have water.
+
+if state is new and altitude is less than 10 then state should be water
+
+;; above the snowline we have snow.
+if state is new and altitude is more than 200 then state should be snow
+
+;; otherwise, we have grassland.
+if state is new then state should be grassland
diff --git a/resources/rulesets/iceage.txt b/resources/rulesets/iceage.txt
new file mode 100644
index 0000000..ca69fa9
--- /dev/null
+++ b/resources/rulesets/iceage.txt
@@ -0,0 +1,65 @@
+## Ruleset which attempts to model retreat of ice after an iceage
+
+if generation is less than 5 then state should be ice
+
+;; Limitations: because the rule language doesn't (yet) allow sophisticated
+;; arithmetic, the ice retreats north to south (southern hemisphere).
+
+## Vegetation rules
+;; rules which populate the world with plants
+
+;; Occasionally, passing birds plant tree seeds into grassland 
+
+if state is grassland then 1 chance in 10 state should be heath
+
+;; heath below the treeline grows gradually into forest, providing browsing pressure is not to high
+
+if state is heath and fertility is more than 10 and altitude is less than 120 then state should be scrub 
+if state is scrub and fertility is more than 20 then 1 chance in 20 state should be forest
+
+;; Forest on fertile land grows to climax
+
+if state is forest and fertility is more than 30 and altitude is less than 70 then state should be climax   
+    
+;; Climax forest occasionally catches fire (e.g. lightning strikes)
+
+if state is climax then 1 chance in 500 state should be fire
+
+;; Climax forest neighbouring fires is likely to catch fire
+if state is climax and some neighbours are fire then 1 chance in 3 state should be fire
+
+;; After fire we get waste
+
+if state is fire then state should be waste
+
+;; And after waste we get pioneer species; if there's a woodland seed
+;; source, it's going to be heath, otherwise grassland.
+
+if state is waste and some neighbours are scrub then state should be heath
+if state is waste and some neighbours are forest then state should be heath
+if state is waste and some neighbours are climax then state should be heath
+if state is waste then state should be grassland
+
+## Potential blockers
+
+;; Woody plants increase soil fertility over time. 
+if state is in heath or scrub or forest or climax then fertility should be fertility + 1
+
+
+## Initialisation rules
+
+;; Rules which deal with state 'new' will waste less time if they're near the
+;; end of the file
+
+if state is new then state should be ice
+
+;; thaw moves gradually southwards (the distinction between 'ice' and 'snow' is
+;; just a hack because I can't do complex arithmetic in rules)
+;; below the waterline ice thaws to water.
+if state is ice and generation is more than y and altitude is less than 10 then state should be water
+;; otherwise it thaws to snow
+if state is ice and generation is more than y then state should be snow
+
+;; thaw moves gradually up the hills
+
+if state is snow and generation is more than altitude then state should be waste
diff --git a/resources/rulesets/settlement.txt b/resources/rulesets/settlement.txt
index 0bc8feb..6d66ed0 100644
--- a/resources/rulesets/settlement.txt
+++ b/resources/rulesets/settlement.txt
@@ -1,3 +1,6 @@
+;; hack to speed up processing on the 'great britain and ireland' map
+if state is water then state should be water
+
 # Human settlement
 
 ;; nomads make their first significant camp near water because of fish and
@@ -5,26 +8,26 @@
 if state is in grassland or heath and more than 3 neighbours are water and generation is more than 20 then state should be camp
 
 ;; sooner or later nomads learn to keep flocks
-if state is in grassland or heath and some neighbours are camp then state should be meadow
+if state is in grassland or heath and some neighbours are camp then state should be pasture
 
 ;; and more herds support more people
-if state is in grassland or heath and more than 2 neighbours are meadow then state should be camp
-if state is meadow and more than 3 neighbours are meadow and fewer than 1 neighbours are camp and fewer than 1 neighbours within 2 are house then state should be camp
+if state is in grassland or heath and more than 2 neighbours are pasture then state should be camp
+if state is pasture and more than 3 neighbours are pasture and fewer than 1 neighbours are camp and fewer than 1 neighbours within 2 are house then state should be camp
 
 ;; the idea of agriculture spreads
-if state is in grassland or heath and some neighbours are meadow and some neighbours within 3 are house then state should be meadow
+if state is in grassland or heath and some neighbours are pasture and some neighbours within 3 are house then state should be pasture
 
 ;; nomads move on
 if state is camp then 1 chance in 5 state should be waste
 
-;; meadow that's too far from a house or camp will be abandoned
-if state is meadow and fewer than 1 neighbours within 3 are house and fewer than 1 neighbours within 2 are camp then state should be heath
+;; pasture that's too far from a house or camp will be abandoned
+if state is pasture and fewer than 1 neighbours within 3 are house and fewer than 1 neighbours within 2 are camp then state should be heath
 
 ;; markets spring up near settlements
-if state is in grassland or meadow and more than 1 neighbours are house then 1 chance in 10 state should be market
+if state is in grassland or pasture and more than 1 neighbours are house then 1 chance in 10 state should be market
 
 ;; good fertile pasture close to settlement will be ploughed for crops
-if state is meadow and fertility is more than 10 and altitude is less than 100 and some neighbours are camp or some neighbours are house then state should be ploughland
+if state is pasture and fertility is more than 10 and altitude is less than 100 and some neighbours are camp or some neighbours are house then state should be ploughland
 
 if state is ploughland then state should be crop
 
@@ -33,25 +36,25 @@ if state is crop then state should be grassland
 
 ;; if there's reliable food available, nomads build permanent settlements
 if state is in camp or abandoned and some neighbours are crop then state should be house
-if state is abandoned and some neighbours are meadow then state should be house
+if state is abandoned and some neighbours are pasture then state should be house
 ;; people camp near to markets
 if state is in waste or grassland and some neighbours are market then state should be camp
 
 ;; a market in a settlement survives
-if state is market and more than 3 neighbours are house then state should be market
 if state is market and some neighbours are inn then state should be market
 if state is market then state should be grassland
 
 ;; a house near a market in a settlement will become an inn
-if state is house and some neighbours are market and more than 1 neighbours are house then state should be inn
+if state is house and some neighbours are market and more than 1 neighbours are house then 1 chance in 5 state should be inn
 ;; but it will need some local custom to survive
-if state is inn and fewer than 2 neighbours are house then state should be house
+if state is inn and fewer than 3 neighbours are house then state should be house
 
 ;; if there aren't enough resources houses should be abandoned
 ;; resources from fishing
 if state is house and more than 2 neighbours are water then state should be house
 ;; from farming
-if state is house and some neighbours are meadow then state should be house
+if state is house and some neighbours are pasture then state should be house
+if state is house and some neighbours are ploughland then state should be house
 if state is house and some neighbours are crop then state should be house
 ;; from the market
 if state is house and some neighbours are market then state should be house
@@ -66,14 +69,14 @@ if state is abandoned then 1 chance in 5 state should be waste
 
 if state is grassland then 1 chance in 10 state should be heath
 
-;; heath below the treeline grows gradually into forest, providing browsing pressure is not to high
+;; heath below the treeline grows gradually into forest
 
-if state is heath and deer are fewer than 6 and altitude is less than 150 then state should be scrub 
+if state is heath and altitude is less than 120 then state should be scrub 
 if state is scrub then 1 chance in 5 state should be forest
 
 ;; Forest on fertile land grows to climax
 
-if state is forest and fertility is more than 5 then state should be climax   
+if state is forest and fertility is more than 5 and altitude is less than 70 then state should be climax   
     
 ;; Climax forest occasionally catches fire (e.g. lightning strikes)
 
@@ -83,12 +86,15 @@ if state is climax then 1 chance in 500 state should be fire
 if state is in climax or camp or house or inn and some neighbours are fire then 1 chance in 3 state should be fire
 
 ;; Climax forest near to settlement may be cleared for timber
-if state is in climax and more than 3 neighbours within 2 are house then state should be waste
+if state is in climax and more than 3 neighbours within 2 are house then state should be scrub
 
 ;; After fire we get waste
 
 if state is fire then state should be waste
 
+;; waste near settlement that is fertile becomes ploughland
+if state is waste and fertility is more than 10 and some neighbours are house or some neighbours are camp then state should be ploughland
+
 ;; And after waste we get pioneer species; if there's a woodland seed
 ;; source, it's going to be heath, otherwise grassland.