No. 1. — Fossil Sponges of the Flint Nodules in the Lower Cretaceous 

 of Texas. By J. A. Merrill. 1 



The following investigation was undertaken as thesis work in the 

 course in Palaeontology in Harvard University, at the suggestion of the 

 instructor, Dr. li. T. Jackson. As the study proceeded, its importance 

 became more apparent and it was thought advisable to extend the. work 

 somewhat and publish it. With the advice and assistance of Professor 

 N. S. Shaler, therefore, careful revision has been made and the results 

 here .presented. So far as I have been able to ascertain, the minute 

 structure of the cretaceous Hints of America has never been studied 

 except in a general way, and nothing whatever has been published on 

 the microscopic organisms composing them. The field is therefore 

 a large as well as a fascinating one, and this effort is intended 

 only as a beginning of what is hoped will prove a fruitful line of 

 inquiry. The flint nodules from which specimens were taken for 

 study were collected in a quarry near Austin, Texas, and brought to 

 Cambridge by Mr. Edward E. Cauthorne. They vary greatly in shape 

 and size ; and, owing, perhaps, to small areas of calcite scattered through 

 the mass, they vary somewhat in hardness. The hardness is often 

 greater than that of glass, and the flint will generally scratch glass. In 

 shape they are spherical, cylindrical, or flat ; and in size they vary from 

 two inches to a foot or more iu diameter. The color is a dense black, 

 with white or gray spots mixed irregularly through it, varying in size 

 from microscopic to that of a pin-head. These spots are generally 

 replacements of organic remains, and, when such, are, in all cases that I 

 examined, chalcedonic silica ; the larger ones showing the concentric 

 structure characteristic of chalcedony. Some of them, however, have 

 shapes so irregular and outlines so indefinite, that they cannot be re- 

 ferred to any particular organic form, although they are most likely 

 replacements. All the spots of calcite examined are small and 

 indefinite in form and outline. They are called calcite because of 

 their behavior in polarized light. The outside of the nodule is com- 

 posed of a layer of chalk about one quarter to three quarters of an inch 



1 Contributions from the Geological Laboratory of the Museum of Comparative 

 Zoology, in charge of N. S. Shaler. 



VOL. XXVIII. — NO. 1. 1 



