An improved contour for logs which are to be assembled one on top of the other for producing walls, etc. for log cabins. The contour includes a pair of plain parallel surfaces, one on the top, and the other on the bottom of the log, as installed. In the preferred embodiment the top surface carries a pair of spaced parallel tongues of trapezoidal cross-section, and the bottom surface carries substantially a mirror image, in the form of two grooves which are adapted to fit over the tongues on the log immediately adjacent below. On either side of the tongues and grooves are two shelves which are approximately horizontal. However, on the top surface they slope at a small angle A downwardly from the horizontal, to their lips at the intersection with the outer contour of the log. Similarly, on the under side, the shelves slope downwardly at a slightly greater angle B so that when one log is placed on top of the other, the two lips will be in contact and will support the one log on top of the other, providing a high unit pressure to promote the exclusion of moisture through the contact.