  For Classical T Tauri Stars (CTTSs), the resonance lines of N V, Si IV, and C
IV, as well as the He II 1640 A line, act as diagnostics of the accretion
process. Here we assemble a large high-resolution dataset of these lines in
CTTSs and Weak T Tauri Stars (WTTSs). We present data for 35 stars: one Herbig
Ae star, 28 CTTSs, and 6 WTTSs. We decompose the C IV and He II lines into
broad and narrow Gaussian components (BC & NC). The most common (50 %) C IV
line morphology in CTTSs is that of a low-velocity NC together with a
redshifted BC. The velocity centroids of the BCs and NCs are such that V_BC > 4
* V_NC, consistent with the predictions of the accretion shock model, in at
most 12 out of 22 CTTSs. We do not find evidence of the post-shock becoming
buried in the stellar photosphere due to the pressure of the accretion flow.
The He II CTTSs lines are generally symmetric and narrow, less redshifted than
the CTTSs C IV lines, by ~10 km/sec. The flux in the BC of the He II line is
small compared to that of the C IV line, consistent with models of the
pre-shock column emission. The observations are consistent with the presence of
multiple accretion columns with different densities or with accretion models
that predict a slow-moving, low-density region in the periphery of the
accretion column. For HN Tau A and RW Aur A, most of the C IV line is
blueshifted suggesting that the C IV emission is produced by shocks within
outflow jets. In our sample, the Herbig Ae star DX Cha is the only object for
which we find a P-Cygni profile in the C IV line, which argues for the presence
of a hot (10^5 K) wind. For the overall sample, the Si IV and N V line
luminosities are correlated with the C IV line luminosities, although the
relationship between Si IV and C IV shows large scatter about a linear
relationship and suggests that TW Hya, V4046 Sgr, AA Tau, DF Tau, GM Aur, and
V1190 Sco are silicon-poor.
