It was made of small juicy clams, scarcely bigger than hazel nuts, mixed with pounded ship biscuit, and salted pork cut up into little flakes; the whole enriched with butter, and plentifully seasoned with pepper and salt.
Now, at least one thing is missing here, which is potato; few chowders are served in New England today without potato in them, and, I would say, there is good reason. Ishmael's chowder is an inferior sort; Melville should have known better.
Here's the way to make chowder: First, start with butter. Many a debate is held over milk or cream, but the answer ought to be obvious: skim the cream, turn it to butter, feed the whey to the animals, and begin your chowder with as much butter as you can. It ought to lie thick in the bottom of the pot. Now, throw into that butter a minced potato or two and simmer it. Minced potato?! Most debates over potato and chowder revolve around chunks, and chunks are optional later in the recipe (I myself like them in moderation, especially when you don't have enough clams), but minced potato is critical to the whole chowder. Add some pepper here, too, for the spice is best cooked deeply into the food, not dashed on top.
Watch that butter and potato until you can see the starch oozing from the potato and thickening up the butter, and that's the point where you toss in some clams, so they can soak up the butter, and a little bit of finely chopped onion, to impart its flavor; after just a bit here, then add the brine or juice of the clam (that will be sufficient salt) and, if you so choose, chunks of potato and even a bit of celery, and any shredded pork (I leave out the pork, myself, but favor a small bit of celery or even celery seed where the vegetable is lacking, and my use of potato depends on the number and qualities of clams: potato is a stretcher), and simmer to thicken and soften. The idea is that the potato startch ought to thicken it up so your chowder is a solidly creamy and thick consistency without the use of any flour or floury substance and without any cream (which you've added as butter).
Potatoless ship biscuit chowder, on the other hand, will tend to be clumpy and watery, not properly thickened, almost as if you'd curdled the milk. And flour imparts a dry gluey taste to the clams.