G 



rated. But they were not enough to show that the layers were 

 themselves composed of lenses nor to make the true structure evi- 

 dent. Moorehead and Leighton point out that the builders piled 

 up the earth several feet and then used the mound for several sea- 

 sons. Thus vegetation had an opportunity to take root, grow and 

 form a soil layer rich in carbon and dark. In some instances 

 the layer is an inch, in others many inches thick. In Asia Minor 

 and Egypt people had a similar habit. When one house fell and 

 was buried by its own roof or by shifting sands, another was often 

 built on the ruins. As a result whole towns arose on the ruins of 

 previous towns and excavations show half a dozen layers built on 

 the oldest layer. 



There are a number of features disclosed in these Cahokia ex- 

 plorations which are worthy of further study. There are certain 

 yellowish brow r n layers half an inch or more in thickness which 

 are called "burnt floors" though they show no sign of fusion. If 

 fire were built on them the fires were small since vitrified or fused 

 masses are wanting. Some of these floors slant at an angle as 

 steep as 45 degrees. Dr. Reinhardt Thiesson says that much of 

 the so-called charcoal in the mounds is rather natural peat or coali- 

 fied wood and much of the so-called ashes are silicifications. The 

 writer finds that many of the samples of "ashes" contain fifty 

 percent of calcareous matter and nothing like true ashes. Dr. R. S. 

 Smith classified the soils collected by the writer, in accordance 

 with usage in the department of soil physics at the University of 

 Illinois. 



The mounds deserve careful study, not only by the archae- 

 ologist who can picture to us the manner of life and mode of 

 thought of the men who built them and used them, but also by the 

 microscopist, chemist, zoologist, physiographer and geologist who 

 can bring a wealth of knowledge and experience to the study. 



A. R. Crook. 

 May 19, 1923. 



