148 Notes on the Geological Position of the Human Skeleton. 
The finding of a tobacco-pipe 12 ft. below tlie surface shows 
us bow poor a measure of age is afforded by mere depth, 
unchecked by other evidence, in the case of remains found in 
recent alluvial deposits. Engineers have estimated the growth 
in thickness of the inundation-mud of the Nile as being at the 
rate of five inches in a century. Consequently an article 
found in it at a depth of 12 ft. might be fairly supposed to be 
more than 2800 years old; while remains that have been 
deposited in a former channel of a river given to frequent 
changes of its course might be found at more than twice that 
depth without having any necessary claim to be considered 
ancient, even in the sense in which we speak of ancient 
history. 
1 
