34 EXTINCT MONSTERS 



York States were made by the soft fragile larvae of insects 

 which existed at an early period in the world's history. 



We now pass on to the consideration of certain impressions in 

 the old Potsdam Sandstone of North America, which have been 

 most carefully studied by the late Sir E. Owen. In the year 

 1851, Logan exhibited before the Geological Society of London a 

 small slab of sandstone showing some footprints, and a plaster 

 cast from a longer surface of similar description. The original, 

 weighing upwards of a ton, is in the Museum at Montreal con- 

 nected with the McGill University The locality where it was 

 found is on the left bank of the Eiver St. Louis, at the village 

 of Beauharnois, on the south side of the St. Lawrence, about 

 twenty miles above the city of Montreal. Owen, in his first 

 paper, came to the conclusion that the tracks were those of a 

 tortoise. But further research caused him to alter this opinion. 

 We only mention that to show how much care is required even 

 on the part of the best naturalists to read the meanings of fossil 

 tracks. A portion of the impressions now under consideration is 

 shown in Fig. 1. They consist of a series of well-defined impres- 

 sions continued in regular succession for four feet, and more ; 

 but only clearly for four feet. In this four feet there are thirty 

 successive groups of footprints on each side of a furrow. The 

 number of prints is not the same in each group. Where they are 

 best marked, as in our figure, we see three prints in one group, 

 two in the next and two in the third, followed by a repetition of 

 the three prints (in our illustration each of the three groups is 

 enclosed in an oval). These three groups (of 3-2-2 impressions) 

 are distinctly repeated in succession along the whole series of 

 tracks on both sides of the furrow. It will be noticed that in 

 each pair of impressions the innermost pair are of equal size, but 

 of the outer ones each is a little bigger than the last. An 



