  Telescope Array (TA) has completed analysis of nearly nine years of data
measuring the atmospheric depth of air shower maximum ($X_{\textrm{max}}$)
utilizing the TA surface detector array and the Black Rock Mesa and Long Ridge
fluorescence detector stations. By using both the surface array and the
fluorescence detector, the geometry and arrival time of air showers can be
measured very precisely providing good resolution in determining
$X_{\textrm{max}}$. $X_{\textrm{max}}$ is directly related to the air shower
primary particle mass and is therefore important for understanding the
composition of ultra high energy cosmic rays (UHECRs). UHECR composition will
help answer questions such as the distance and location of their sources. We
discuss the experimental apparatus, analysis method, and $X_{\textrm{max}}$
data collected. We compare the energy dependent distributions of the observed
data to detailed Monte Carlo simulations of four chemical species, then test
which individual species are not compatible with the data through an analysis
of the shapes of the distributions. We also discuss the present state of
composition analysis and interpretation between the Auger and TA experiments.
These are the two largest UHECR observatories in the world with large exposures
and should shed light on UHECR composition.
