The below text is copied from the Bitcoin Developer Reference at bitcoin.org:
If a block has three or more transactions, intermediate merkle tree rows are formed. The TXIDs are placed in order and paired, starting with the coinbase transaction’s TXID. Each pair is concatenated together as 64 raw bytes and SHA256(SHA256()) hashed to form a second row of hashes. If there are an odd (non-even) number of TXIDs, the last TXID is concatenated with a copy of itself and hashed. If there are more than two hashes in the second row, the process is repeated to create a third row (and, if necessary, repeated further to create additional rows). Once a row is obtained with only two hashes, those hashes are concatenated and hashed to produce the merkle root.
I'm trying to use this logic to recreate the merkle root for block #100000. There are 4 transactions in this block. I start by copying the transaction hash for the coinbase transaction and the one following back-to-back into a Sha256 calculator to get the hash. Then I hash that hash one more time: Sha256(sha256()). I repeat that procedure one more time with the second two transactions in the block. Finally, I repeat the procedure again using the resulting hashes to obtain the Merkle Root. Unfortunately, this doesn't tie to the Merkle Root shown in the block header at blockchain.info.
Can someone explain where I went wrong?