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tokens: the WISE images, which are likely the shock fronts. At the angular resolution of the H i data, this appears to be the case. Figure 5. Position–velocity slice for clouds G228 and G230. The left panel is the unWISE mid-infrared image, with a dashed green line illustrating the path along which the slice was made. The right panel shows the brightness temperature of the 21 cm line, with the horizontal axis being position along the slice (starting from 0 at the top of the green line in the left panel), and the vertical axis being the velocity (0.8 km s −1 pixels, spanning 50 km s −1 ). 4.2. Atomic and Molecular Content Comparing the Planck and GASS surveys highlights further the drastic differences between the G228 and G230. Figure 6 shows that G230 has a far higher amount of dust per unit atomic gas than G228. We showed earlier that both G228 and G230 contain CO in their cores, with central velocity and width similar to those of the narrow H i component, and CO core brightness comparable between the two clouds (Reach et al. 1994 ). Figure 6. Comparison of dust optical depth and H i column density for G228 and G230. The purple scale bar is 1° long (1.75 pc if the cloud is at a distance of 100 pc). The left panel shows the dust image, and the right panel shows the scatter-plot. Subsets of the data are shaded in color on the left image and have colored symbols on the right. In red are the points with the highest excess of dust optical depth compared to H i column density; these locations are concentrated in cloud G230, where CO was also detected. In green are the points selected to have the highest H i column density. The H i peak is in G228, and not coincident with the dust peak, which is in G230. In blue are the points selected in the southern “tail” of the image, south of G228 and G230. This region has roughly the same dust-versus-gas trend as the rest of the image and is normal, diffuse atomic gas. This figure, and similar ones in this paper, was made using the package glue (Beaumont et al. 2015 ). The Planck and GASS surveys show that the amount of dust per unit atomic gas is radically different between G228 and G230. If we use the gas column density from the H i 21 cm line and the dust optical depth from far-infrared emission (see Equation (4) of Reach et al. 2015 ), the atomic gas-to-dust ratio is [G/D] = 84 in the regions surrounding the clouds, [G/D] = 55 in G228, and [G/D] = 12 in G230. If the total gas-to-dust ratio is 84 everywhere, then there is significant non-atomic gas in both clouds. The amount of this “dark” gas per unit atomic gas (Equation (7) of Reach et al. 2015 ) is f dark = 1.5 in G228 and f dark = 7 in G230. There is no large-scale CO emission from the main bodies of the clouds in the Planck CO survey, which sets a limit W (CO) 7 K km s −1 on widespread CO. But we did detect CO from the cloud cores using ground-based telescopes (Reach et al. 1994 ); the CO brightness was W (CO) = 2.1 K km s −1 . Mapping observations showed