There appears to be considerable confusion with regard to the Carrickstone. Some say it is a Roman altar around 2000 years old. Others say it is a grave marker of a well known local Covenanter of the time. Here are some descriptions and theories as to the origins of the stone. Take your pick. 

On Carrickstone Farm is a large stone called the 'Standing Stone'. Though it bears no inscription, it has the appearance of a Roman altar. It has a hole in it, where, tradition says, Robert the Bruce planted his standard before the battle of Bannockburn.
NSA 1845 (J Watson)

A stone, standing on a knoll overlooking Dullatur and Cumbernauld, is said to have been a Roman altar. 'It is of buff coloured sand stone, and measures 3ft 1in in height, and 2ft 4ins by 1ft 9ins in breadth and width upon the top, narrowing considerably in the middle of its height, and expanding again to the bottom.'
In the top are some 'cup markings'. The 2 larger cups are about 8ins in diameter and 4 1/2ins in depth; the 2 smaller do not exceed 3ins in diameter.
W A Donelly 1897

This stone stands upon a stone base within a small fenced enclosure. It strongly resembles a Roman altar, with concave sides and ribbed capital and base. The top is pitted with 2 large, and 2 small "cups" - probably formed by both weathering and mutilation. The stone measures 0.4 x 0.6 x 4.1m high. The first part of a 19th century date can be faintly read on the south face.
The letters "CAR---" can be faintly traced on one of the ribs of the head of the stone, on the north face, but would appear to be of modern origin.

"Having been asked whether the stone was called after the farm of Carrickstone, on which it stands, or whether the farm had received its name from the presence of this particular stone, I revisited Dullatur and procured some further information. It seems that the present generation has confused this stone with another which was formerly called the Carrick Stone. The latter was a large slab, which lay horizontally on the ground at the foot of a field about 200 yards in a direct line from the front door of Carrickstone farm-house, and at the base of the slope of the field. This stone, as described to me, was a rudely dressed slab of freestone, having inscribed on its surface, in large and boldly incised letters, the one word CARRICK, and the local tradition said that it marked the grave of a noted Covenanter who was killed and buried here."