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<jats:title>ABSTRACT</jats:title> <jats:p>For Classical T Tauri Stars (CTTSs), the resonance doublets of N <jats:sc>v</jats:sc>, Si <jats:sc>iv</jats:sc>, and C <jats:sc>iv</jats:sc>, as well as the He <jats:sc>ii</jats:sc> 1640 Å line, trace hot gas flows and act as diagnostics of the accretion process. In this paper we assemble a large high-resolution, high-sensitivity data set of these lines in CTTSs and Weak T Tauri Stars (WTTSs). The sample comprises 35 stars: 1 Herbig Ae star, 28 CTTSs, and 6 WTTSs. We find that the C <jats:sc>iv</jats:sc>, Si <jats:sc>iv</jats:sc>, and N <jats:sc>v</jats:sc> lines in CTTSs all have similar shapes. We decompose the C <jats:sc>iv</jats:sc> and He <jats:sc>ii</jats:sc> lines into broad and narrow Gaussian components (BC and NC). The most common (50%) C <jats:sc>iv</jats:sc> line morphology in CTTSs is that of a low-velocity NC together with a redshifted BC. For CTTSs, a strong BC is the result of the accretion process. The contribution fraction of the NC to the C <jats:sc>iv</jats:sc> line flux in CTTSs increases with accretion rate, from ∼20% to up to ∼80%. The velocity centroids of the BCs and NCs are such that <jats:italic>V</jats:italic> <jats:sub>BC</jats:sub> ≳ 4 <jats:italic>V</jats:italic> <jats:sub>NC</jats:sub>, 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 <jats:sc>ii</jats:sc> CTTSs lines are generally symmetric and narrow, with FWHM and redshifts comparable to those of WTTSs. They are less redshifted than the CTTSs C <jats:sc>iv</jats:sc> lines, by ∼10 km s<jats:sup>−1</jats:sup>. The amount of flux in the BC of the He <jats:sc>ii</jats:sc> line is small compared to that of the C <jats:sc>iv</jats:sc> line, and we show that this is consistent with models of the pre-shock column emission. Overall, 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 <jats:sc>iv</jats:sc> line is blueshifted suggesting that the C <jats:sc>iv</jats:sc> 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 <jats:sc>iv</jats:sc> line, which argues for the presence of a hot (10<jats:sup>5</jats:sup> K) wind. For the overall sample, the Si <jats:sc>iv</jats:sc> and N <jats:sc>v</jats:sc> line luminosities are correlated with the C <jats:sc>iv</jats:sc> line luminosities, although the relationship between Si <jats:sc>iv</jats:sc> and C <jats:sc>iv</jats:sc> 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, while CV Cha, DX Cha, RU Lup, and RW Aur may be silicon-rich.</jats:p>