About the Surface Merge Tool
You can use the Merge tool to merge two quilts or surfaces by intersecting or joining them. The resultant quilt becomes the primary quilt and inherits the ID of the primary quilt. If you delete the merged feature, the original quilts remain.
You can also merge two nodes that represent valid quilts. To perform a merge, select two top-level quilt nodes on the Geometry and Topology Structure Tree, right-click, and click Merge on the shortcut menu or click 
Merge on the Structure tab. When you merge two nodes, a new top-level merge node is created and the selected nodes become sub-nodes of the merge node.
Merge on the Structure tab. When you merge two nodes, a new top-level merge node is created and the selected nodes become sub-nodes of the merge node.The target node for the Merge operation is determined by the following conditions:
• If one of the selected nodes is a body node and the other is a quilt or a leaf surface node, the body node is the target node.
• If a quilt and a surface node is selected, the quilt node is the target node.
• If two or more of the same kind of nodes are selected, the first selected node is the target node.
• If the nodes of the same type were selected when the import feature was being redefined with the import feature set to Add Bodies, one of the nodes that is owned by the import feature is the target node regardless of the order of selection.
The sub-node of the Merge node that represents the original target node of the Merge operation retains the generic Component #### name. The target node retains its Solid option setting even if the other node selected for the merge operation has a different Solid option setting. The node that is not the target retains its name, whether read from the source file, assigned by the user after import, or the generic Component ####. The merged node retains the generic name of the target node. Alternatively, it may take the system-assigned name, the name of the node as read from the source file, or the name assigned by the user after import.