A drumlin is deposited till that has been streamlined in the direction of continental ice movement. It has a blunt and steeper slope at the upstream end and a tapered one downstream.
According to Arthur Holmes, drumlins are oddly shaped, resembling half an egg or the convex side of a teaspoon. They are commonly found in swarms as many as 100 or more popularly termed a basket of eggs.
In profile drumlin is in contrast to a roche moutonnee. Some drumlins which contain heterogeneous collection of drift show a degree of stratification. However, most drumlins do not show internal structure.
The most important feature of a drumlin is that it is elongated in the direction of ice flow and its broad, steep noses face the direction from which the ice advanced. Its gently sloping narrow tail points in the direction of ice flow.
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Drumlins are found in large numbers in Ireland, and in the states of New York and Wisconsin. The length of a drumlin varies from half a kilometer to about five kilometers. Drumlins are generally 30 to 200 meters high.
The formation of a drumlin is not yet clear. There are two schools having contrasting opinions in this regard.
Some drumlins appear to be smoothed erosional features, while others seem to have been formed by the plastering of layer upon layer of compact clay. What started such deposition is not yet clear.