296 Shuler — Dinosaur Tracks in the Glen Rose Limestone. 



A microscopic examination shows that both the indurated 

 layer with the tracks and the shale layer above it contain finely 

 comminuted angular fragments of quartz, which in the shale 

 measure up to 1/10 mm., while in the limestone only up 

 to 1/50 mm. In thin section the limestone layer shows an 

 occasioual minute bivalve shell in a ground mass of fine granu- 

 lar calcite w^ith fragments of quartz and clay material. 



The common association of dinosaur tracks has been with 

 sandstones and shales, rocks which bear visible evidence of 



Fig. 2. 



Fig. 2. Near view of Dinosaur track in limestone. 



littoral conditions. But the dinosaur tracks near Glen Rose, 

 Texas, are found in a hard white limestone, which at the time 

 of the passing of the dinosaur must have been in the form of 

 a stiff, tenacious lime mud forming a surface layer of about 

 three inches into which the foot pressed to depths of two to 

 two and a half inches. Had no dinosaur tracks been found the 

 section would probably have been interpreted as having been 

 laid down in deep marine water and at a distance from shore, 

 since no part of the section shows a calcium carbonate content 

 less than 33 per cent. 



What then were the conditions under which the tracks were 

 made ? First of all, the dinosaur was walking on a mud surface, 



