The tuffs which in the southern part of the basin underlie the less basic lavas differ in some respects from those which further north are associated with the Upper Limestones. They are green, sometimes dull purplish-red, finely granular rocks, made up in large part of andesitic debris. They are full of loose felspar crystals, minute, somewhat rounded and subangular lapilli of andesite or some less basic lava, together with bits of grit and baked shale. Though generally much decomposed, they are sometimes compact enough to be used for building-stone. Under the microscope these tuffs are seen to abound in andesite-lapilli, with a few pieces of felsitic rocks enclosed in an opaque base, through which are scattered broken felspars and occasional vesicular lapilli. [Illustration: Fig. 193.--Section in quarry on roadside east of Limerick close to viaduct of the Limerick and Erris Railway. 1. Limestone; 2. Calcareous tuff; 3. Ashy limestone or calcareous tuff.] The tuffs around Limerick, interbedded with the Black (Upper) Limestone, are distinguished by a scarcity of andesitic debris, by their persistent dull greenish-grey colour, and more particularly by the abundance of minute lapilli and larger fragments of an epidote-green, finely vesicular, easily sectile basic pumice. Under the microscope much of this material is found to be an altered basic glass of the nature of palagonite. These tuffs are in evident relation with the more basic lavas that accompany them. The manner in which they alternate with the black limestone shows that the conditions for the eruption of this more basic detritus continued to be very similar to those that existed when the andesitic tuffs were ejected. As a good illustration of this feature the accompanying section (Fig. 193) is given from a quarry on the side of the high-road between Limerick and Annacotty. The total depth of strata here represented is about 15 feet. The black limestone at the bottom is a tolerably pure calcareous rock. It is divided into bands by thin partings of a fine greenish calcareous tuff, each marking a brief discharge of ashes from some neighbouring vent. Half-way up the succession of strata, the ashy material rapidly increases until it usurps the place of the limestone, though its calcareous composition shows that the accumulation of calcareous sediment had not been entirely suspended during the eruption of ash. Among these tuffs I have noticed fragments of fine, dark, flinty felsite, grit and other rocks. The stones are for the most part small, but vary up to blocks occasionally a foot in diameter.