diff --git a/README_CATERVA_METALAYER.rst b/README_CATERVA_METALAYER.rst
index 745aaf76..40160733 100644
--- a/README_CATERVA_METALAYER.rst
+++ b/README_CATERVA_METALAYER.rst
@@ -5,15 +5,16 @@ Caterva is storing persistently its information about shapes and partition shape
 
 Caterva metalayer follows the msgpack format::
 
-    |-0-|-1-|-2-|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|
-    | 9X| nd| 9X| shape          | 9X| partshape      |
-    |---|---|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|
-      ^   ^   ^                     ^
-      |   |   |                     |
-      |   |   |                     +--[msgpack] positive fixnum for the number of dimensions (nd, up to 127)
-      |   |   +---[msgpack] fixarray with X=nd elements
-      |   +------[msgpack] positive fixnum for the number of dimensions (nd, up to 127)
-      +---[msgpack] fixarray with X=3 elements
+    |-0-|-1-|-2-|-3-|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|
+    | 9X| nd| nd| 9X| shape          | 9X| partshape      | 9X| blockshape     |
+    |---|---|---|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|
+      ^   ^   ^    ^                    ^                    ^
+      |   |   |    |                    |                    +--[msgpack] positive fixnum for nd
+      |   |   |    |                    +--[msgpack] positive fixnum for nd
+      |   |   |    +--[msgpack] fixarray with X=nd elements
+      |   |   +--[msgpack] positive fixnum for the number of dimensions (nd, up to 127)
+      |   +--[msgpack] positive fixnum for the metalayer format version (up to 127)
+      +---[msgpack] fixarray with X=5 elements
 
 The shape section
 -----------------
@@ -26,8 +27,8 @@ This section is meant to store the actual shape info.  There are as many fields
       ^                ^                      ^
       |                |                      |
       |                |                      +--[msgpack] int64
-      |                +------[msgpack] int64
-      +---[msgpack] int64
+      |                +--[msgpack] int64
+      +--[msgpack] int64
 
 The partshape section
 ---------------------
@@ -40,5 +41,19 @@ This section is meant to store the actual partition shape info.  There are as ma
       ^                ^                      ^
       |                |                      |
       |                |                      +--[msgpack] int32
-      |                +------[msgpack] int32
-      +---[msgpack] int32
+      |                +--[msgpack] int32
+      +--[msgpack] int32
+
+The blockshape section
+---------------------
+
+This section is meant to store the block shape info inside the partition.  There are as many fields as `nd` dimensions::
+
+    |---|--4 bytes---|---|--4 bytes---|~~~~~|---|--4 bytes---|
+    | d2| first_dim  | d2| second_dim | ... | d2| last_dim   |
+    |---|------------|---|------------|~~~~~|---|------------|
+      ^                ^                      ^
+      |                |                      |
+      |                |                      +--[msgpack] int32
+      |                +--[msgpack] int32
+      +--[msgpack] int32