SUMMARY A small area of Lower Carboniferous (early Brigantian) Limestone in a coastal inlet in the south of the Isle of Man contains boulders of pale bioclastic limestone lying upon and overlain by thin undulating beds of dark calcareous mudstone. It is shown that during deposition of this facies the sea bed dipped towards a syn-sedimentary fault on the north side of the inlet where approximately 3m of normal movement occurred prior to its deposition. 50m to the south, a limebank developed above the crest of a small rollover anticline in the hanging wall of the fault. Instability of this structure led to an episode of sediment collapse. A density flow, containing blocks and boulders of pale limestone, slid northwards over black muddy sediments that were accumulating in the deeper water close to the fault. Both lithologies also show evidence of soft sediment deformation. This study shows that carbonate boulder beds and other fault-related structures can be extremely local in nature.

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Macroinvertebrate assemblages and environmental variables were evaluated as part of the Idaho statewide surface-water quality monitoring program during 1996-98. Two assessment approaches were used to evaluate the macroinvertebrate data collected from Idaho rivers-biological metrics and multivariate statistical analyses. A total of 247 macroinvertebrate taxa were identified in semiquantitative riffle habitat (richest targeted habitat; RTH) and qualitative multiple habitat (QMH) samples, which were collected from 40 sampling sites. Riffles supported most of the taxa collected at all sites. One hundred and eighty-four taxa (74 percent of total taxa) were identified in the RTH samples. Taxa considered abundant in RTH samples included Oligochaeta, Baetis tricaudatus , Hydropsyche , Simuliidae, Chironomidae pupae, Cricotopus , Eukiefferiella , and Orthocladius complex. Comparisons of RTH and QMH sample types indicated little difference in various metrics evaluated; either sample type could be used to evaluate biological condition. Fourteen coldwater taxa were collected during this study at 12 sampling sites, representing only about 6 percent of all taxa collected and a frequency of occurrence of 30 percent for all sites. An evaluation of the Idaho Department of Environmental Quality invertebrate river index (IRI) identified statistically significant differences between highand low-quality sites, providing evidence that the index can successfully discriminate impairment. IRI scores for all sampling sites identified 25 percent of the sites with poor biotic condition and 68 percent with good biotic condition. Maximum temperatures at 62 percent of all sampling sites exceeded Idaho's instantaneous coldwater temperature criteria of 22 ° C. No correspondence was evident between ecoregion percentages upstream from each site and macroinvertebrate assemblages. Multivariate analyses of RTH samples identified various environmental variables operating at different spatial scales that affect the macroinvertebrate assemblages in Idaho rivers. Six environmental variables-percent forested land, percent agricultural land, urban land, maximum water temperature, percent substrate fines, and stream gradient-were significant in describing variance in the macroinvertebrate assemblages. Two distinct groups of sites and associated taxa were identified: one represented high-gradient, coldwater, forested and rangeland sites, and the other represented sites influenced by human disturbance, indicated by increased percent substrate fines and increased water temperatures typically associated with agricultural and (or) urban land uses.

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