diff --git a/src/Soil-Core/SoilBasicBTree.class.st b/src/Soil-Core/SoilBasicBTree.class.st
index 08593d0f..337b3235 100644
--- a/src/Soil-Core/SoilBasicBTree.class.st
+++ b/src/Soil-Core/SoilBasicBTree.class.st
@@ -1,9 +1,6 @@
 Class {
 	#name : #SoilBasicBTree,
-	#superclass : #Object,
-	#instVars : [
-		'store'
-	],
+	#superclass : #SoilIndex,
 	#category : #'Soil-Core-Index-BTree'
 }
 
@@ -20,55 +17,6 @@ SoilBasicBTree >> asCopyOnWrite [
 		yourself 
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> at: key [ 
-	^ self 
-		at: key 
-		ifAbsent: [ KeyNotFound signalFor: key in: self  ] 
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> at: anObject ifAbsent: aBlock [
-	^ (self find: anObject) 
-		ifNotNil: [:node | node value ]
-		ifNil: [ aBlock value ] 
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> at: aKeyObject put: anObject [
-
-	self newIterator 
-		at: aKeyObject 
-		put: anObject.
-
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> atIndex: anInteger [
-	^ self newIterator atIndex: anInteger 
-]
-
-{ #category : #'open/close' }
-SoilBasicBTree >> close [
-	self store close
-]
-
-{ #category : #private }
-SoilBasicBTree >> find: aString [ 
-	^ self newIterator 
-		find: (aString asSkipListKeyOfSize: self keySize) asInteger
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> first [
-	^ self newIterator first
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> first: anInteger [
-	^ self newIterator first: anInteger
-]
-
 { #category : #accessing }
 SoilBasicBTree >> firstPage [
 	^ self headerPage
@@ -79,16 +27,6 @@ SoilBasicBTree >> flush [
 	self store flush
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> flushCachedPages [
-	store flushCachedPages
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> headerPage [
-	^ self store headerPage
-]
-
 { #category : #initialization }
 SoilBasicBTree >> initializeFilesystem [ 
 	self store initializeFilesystem
@@ -104,21 +42,6 @@ SoilBasicBTree >> initializeHeaderPage [
 	self store pageAt: rootIndexPage index put: rootIndexPage
 ]
 
-{ #category : #testing }
-SoilBasicBTree >> isEmpty [
-	^ self store headerPage isEmpty
-]
-
-{ #category : #testing }
-SoilBasicBTree >> isRegistered [
-	^ self subclassResponsibility
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> keySize [
-	^ self headerPage keySize
-]
-
 { #category : #accessing }
 SoilBasicBTree >> keySize: anInteger [
 	self headerPage keySize: anInteger.
@@ -126,16 +49,6 @@ SoilBasicBTree >> keySize: anInteger [
 	self rootPage keySize: anInteger
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> last [
-	^ self newIterator last
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> lastPage [
-	^ self newIterator lastPage
-]
-
 { #category : #accessing }
 SoilBasicBTree >> maxLevel: anIntegeer [
 	"ignored, this allows to switch SkiList and BTree easily"
@@ -202,21 +115,11 @@ SoilBasicBTree >> open [
 	self store open
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> pageAt: anInteger [ 
-	^ self store pageAt: anInteger 
-]
-
 { #category : #initialization }
 SoilBasicBTree >> pageClass [
 	^ SoilBTreeDataPage
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> pageSize [
-	^ 4 * 1024
-]
-
 { #category : #accessing }
 SoilBasicBTree >> pages [
 	^ self store pages
@@ -227,13 +130,6 @@ SoilBasicBTree >> readPageFrom: aStream [
 	^ SoilBTreePage readPageFrom: aStream keySize: self keySize valueSize: self valueSize
 ]
 
-{ #category : #removing }
-SoilBasicBTree >> removeKey: key [ 
-	^ self
-		removeKey: key 
-		ifAbsent: [ KeyNotFound signalFor: key in: self ]
-]
-
 { #category : #removing }
 SoilBasicBTree >> removeKey: aString ifAbsent: aBlock [
 	| page index key |
@@ -251,12 +147,6 @@ SoilBasicBTree >> rootPage [
 	^ self store pageAt: 2
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> size [
-	"We iterate over all elements to get the size. Slow!"
-	^ self newIterator size 
-]
-
 { #category : #splitting }
 SoilBasicBTree >> splitIndexPage: page [ 
 	| newPage |
@@ -276,33 +166,6 @@ SoilBasicBTree >> splitPage: page [
 	^ newPage 
 ]
 
-{ #category : #accessing }
-SoilBasicBTree >> store [
-	^ store ifNil: [ 
-		store := self newFileStore ]
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> store: anObject [
-	anObject index: self.
-	store := anObject
-]
-
-{ #category : #converting }
-SoilBasicBTree >> thePersistentInstance [
-	^ self subclassResponsibility
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> valueSize [
-	^ self headerPage valueSize
-]
-
-{ #category : #accessing }
-SoilBasicBTree >> valueSize: anInteger [
-	self headerPage valueSize: anInteger
-]
-
 { #category : #writing }
 SoilBasicBTree >> writePages [
 	self store flushPages
diff --git a/src/Soil-Core/SoilBasicSkipList.class.st b/src/Soil-Core/SoilBasicSkipList.class.st
index 0961f192..64239e03 100644
--- a/src/Soil-Core/SoilBasicSkipList.class.st
+++ b/src/Soil-Core/SoilBasicSkipList.class.st
@@ -1,9 +1,6 @@
 Class {
 	#name : #SoilBasicSkipList,
-	#superclass : #Object,
-	#instVars : [
-		'store'
-	],
+	#superclass : #SoilIndex,
 	#category : #'Soil-Core-Index-SkipList'
 }
 
@@ -13,107 +10,17 @@ SoilBasicSkipList class >> isAbstract [
 	^ self == SoilBasicSkipList
 ]
 
-{ #category : #private }
-SoilBasicSkipList >> at: key [ 
-	^ self 
-		at: key 
-		ifAbsent: [ KeyNotFound signalFor: key in: self ]
-]
-
-{ #category : #private }
-SoilBasicSkipList >> at: anObject ifAbsent: aBlock [
-	^ (self find: anObject) 
-		ifNotNil: [:node | node value ]
-		ifNil: [ aBlock value ] 
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> at: aKeyObject put: anObject [
-	self newIterator 
-		at: aKeyObject 
-		put: anObject.
-
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> atIndex: anInteger [
-	^ self newIterator atIndex: anInteger 
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> basicAt: key put: anObject [
-	^ self newIterator 
-		basicAt: key 
-		put: anObject 
-]
-
-{ #category : #enumerating }
-SoilBasicSkipList >> do: aBlock [
-	self newIterator do: aBlock
-]
-
-{ #category : #private }
-SoilBasicSkipList >> find: aString [ 
-	^ self newIterator 
-		find: (aString asSkipListKeyOfSize: self keySize) asInteger
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> first [
-	^ self newIterator first
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> first: anInteger [
-	^ self newIterator first: anInteger
-]
-
 { #category : #accessing }
 SoilBasicSkipList >> firstPage [
 	^ self store pageAt: 1
 ]
 
-{ #category : #accessing }
-SoilBasicSkipList >> flushCachedPages [
-	store flushCachedPages
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> headerPage [
-	^ self store headerPage
-]
-
-{ #category : #testing }
-SoilBasicSkipList >> isEmpty [
-	^ self store headerPage isEmpty
-]
-
-{ #category : #testing }
-SoilBasicSkipList >> isRegistered [
-	^ self subclassResponsibility
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> keySize [
-	^ self headerPage keySize
-]
-
 { #category : #accessing }
 SoilBasicSkipList >> keySize: anInteger [
 	anInteger isZero ifTrue: [ Error signal: 'keySize cannot be zero yet' ].
 	self headerPage keySize: anInteger
 ]
 
-{ #category : #accessing }
-SoilBasicSkipList >> last [
-	^ self newIterator last
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> lastPage [
-	^ self newIterator lastPage
-]
-
 { #category : #accessing }
 SoilBasicSkipList >> maxLevel [
 
@@ -126,38 +33,16 @@ SoilBasicSkipList >> maxLevel: anInteger [
 	self headerPage maxLevel: anInteger 
 ]
 
-{ #category : #'public/accessing' }
+{ #category : #'instance creation' }
 SoilBasicSkipList >> newIterator [ 
 	^ SoilSkipListIterator on: self 
 ]
 
-{ #category : #'instance creation' }
-SoilBasicSkipList >> newPage [
-	^ self subclassResponsibility
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> pageAt: anInteger [ 
-	^ self store pageAt: anInteger 
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> pageSize [
-	^ 4 * 1024
-]
-
 { #category : #accessing }
 SoilBasicSkipList >> pages [
 	^ self store pages
 ]
 
-{ #category : #removing }
-SoilBasicSkipList >> removeKey: key [ 
-	^ self
-		removeKey: key 
-		ifAbsent: [ KeyNotFound signalFor: key in: self ]
-]
-
 { #category : #removing }
 SoilBasicSkipList >> removeKey: aString ifAbsent: aBlock [
 	| page index key |
@@ -170,12 +55,6 @@ SoilBasicSkipList >> removeKey: aString ifAbsent: aBlock [
 		ifFalse: [ aBlock value ]
 ]
 
-{ #category : #accessing }
-SoilBasicSkipList >> size [
-	"We iterate over all elements to get the size. Slow!"
-	^ self newIterator size 
-]
-
 { #category : #private }
 SoilBasicSkipList >> splitPage: aIterator forKey: aKey [
 	| newPage page |
@@ -201,35 +80,6 @@ SoilBasicSkipList >> splitPage: aIterator forKey: aKey [
 	^ newPage 
 ]
 
-{ #category : #accessing }
-SoilBasicSkipList >> store [
-	^ store ifNil: [ 
-		store := self newFileStore ]
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> store: anObject [
-	anObject index: self.
-	store := anObject
-]
-
-{ #category : #converting }
-SoilBasicSkipList >> thePersistentInstance [
-	^ self subclassResponsibility
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> valueSize [
-	"^ 8"
-	^ self headerPage valueSize
-]
-
-{ #category : #accessing }
-SoilBasicSkipList >> valueSize: anInteger [ 
-	"valueSize := anInteger"
-	self headerPage valueSize: anInteger 
-]
-
 { #category : #enumerating }
 SoilBasicSkipList >> values [ 
 	| values |
diff --git a/src/Soil-Core/SoilIndex.class.st b/src/Soil-Core/SoilIndex.class.st
new file mode 100644
index 00000000..f203f6aa
--- /dev/null
+++ b/src/Soil-Core/SoilIndex.class.st
@@ -0,0 +1,172 @@
+Class {
+	#name : #SoilIndex,
+	#superclass : #Object,
+	#instVars : [
+		'store'
+	],
+	#category : #'Soil-Core-Index-Common'
+}
+
+{ #category : #private }
+SoilIndex >> at: key [ 
+	^ self 
+		at: key 
+		ifAbsent: [ KeyNotFound signalFor: key in: self ]
+]
+
+{ #category : #accessing }
+SoilIndex >> at: anObject ifAbsent: aBlock [
+	^ (self find: anObject) 
+		ifNotNil: [:node | node value ]
+		ifNil: [ aBlock value ] 
+]
+
+{ #category : #accessing }
+SoilIndex >> at: aKeyObject put: anObject [
+	self newIterator 
+		at: aKeyObject 
+		put: anObject
+]
+
+{ #category : #accessing }
+SoilIndex >> atIndex: anInteger [
+	^ self newIterator atIndex: anInteger 
+]
+
+{ #category : #accessing }
+SoilIndex >> basicAt: key put: anObject [
+	^ self newIterator 
+		basicAt: key 
+		put: anObject 
+]
+
+{ #category : #'open/close' }
+SoilIndex >> close [
+	self store close
+]
+
+{ #category : #enumerating }
+SoilIndex >> do: aBlock [
+	self newIterator do: aBlock
+]
+
+{ #category : #private }
+SoilIndex >> find: aString [ 
+	^ self newIterator 
+		find: (aString asSkipListKeyOfSize: self keySize) asInteger
+]
+
+{ #category : #accessing }
+SoilIndex >> first [
+	^ self newIterator first
+]
+
+{ #category : #accessing }
+SoilIndex >> first: anInteger [
+	^ self newIterator first: anInteger
+]
+
+{ #category : #accessing }
+SoilIndex >> flushCachedPages [
+	store flushCachedPages
+]
+
+{ #category : #accessing }
+SoilIndex >> headerPage [
+	^ self store headerPage
+]
+
+{ #category : #testing }
+SoilIndex >> isEmpty [
+	^ self store headerPage isEmpty
+]
+
+{ #category : #testing }
+SoilIndex >> isRegistered [
+	^ self subclassResponsibility
+]
+
+{ #category : #accessing }
+SoilIndex >> keySize [
+	^ self headerPage keySize
+]
+
+{ #category : #accessing }
+SoilIndex >> last [
+	^ self newIterator last
+]
+
+{ #category : #accessing }
+SoilIndex >> lastPage [
+	^ self newIterator lastPage
+]
+
+{ #category : #'instance creation' }
+SoilIndex >> newFileStore [
+	^ self subclassResponsibility
+]
+
+{ #category : #'instance creation' }
+SoilIndex >> newIterator [
+	^ self subclassResponsibility
+]
+
+{ #category : #'instance creation' }
+SoilIndex >> newPage [
+	^ self subclassResponsibility
+]
+
+{ #category : #accessing }
+SoilIndex >> pageAt: anInteger [ 
+	^ self store pageAt: anInteger 
+]
+
+{ #category : #accessing }
+SoilIndex >> pageSize [
+	^ 4 * 1024
+]
+
+{ #category : #removing }
+SoilIndex >> removeKey: key [ 
+	^ self
+		removeKey: key 
+		ifAbsent: [ KeyNotFound signalFor: key in: self ]
+]
+
+{ #category : #'instance creation' }
+SoilIndex >> removeKey: aString ifAbsent: aBlock [
+	^ self subclassResponsibility
+]
+
+{ #category : #accessing }
+SoilIndex >> size [
+	"We iterate over all elements to get the size. Slow!"
+	^ self newIterator size 
+]
+
+{ #category : #accessing }
+SoilIndex >> store [
+	^ store ifNil: [ 
+		store := self newFileStore ]
+]
+
+{ #category : #accessing }
+SoilIndex >> store: anObject [
+	anObject index: self.
+	store := anObject
+]
+
+{ #category : #converting }
+SoilIndex >> thePersistentInstance [
+	^ self subclassResponsibility
+]
+
+{ #category : #accessing }
+SoilIndex >> valueSize [
+	^ self headerPage valueSize
+]
+
+{ #category : #accessing }
+SoilIndex >> valueSize: anInteger [
+	self headerPage valueSize: anInteger
+]
diff --git a/src/Soil-Core/SoilSkipList.class.st b/src/Soil-Core/SoilSkipList.class.st
index 2c2e996b..d6d0660b 100644
--- a/src/Soil-Core/SoilSkipList.class.st
+++ b/src/Soil-Core/SoilSkipList.class.st
@@ -21,17 +21,12 @@ SoilSkipList >> asCopyOnWrite [
 		yourself 
 ]
 
-{ #category : #'opening/closing' }
-SoilSkipList >> close [
-	self store close
-]
-
 { #category : #deleting }
 SoilSkipList >> destroy [
 	path ensureDelete 
 ]
 
-{ #category : #accessing }
+{ #category : #deleting }
 SoilSkipList >> flush [
 	self store flush
 ]
@@ -54,7 +49,7 @@ SoilSkipList >> initializeParametersFrom: aSoilSkipList [
 		valueSize: aSoilSkipList valueSize
 ]
 
-{ #category : #private }
+{ #category : #testing }
 SoilSkipList >> isPersistent [
 	^ path notNil
 ]
@@ -136,7 +131,6 @@ SoilSkipList >> thePersistentInstance [
 
 { #category : #accessing }
 SoilSkipList >> valueSize [
-	"^ 8"
 	^ valueSize ifNil: [ 
 		valueSize := super valueSize ]
 ]