of two generations of structures. Description The units of the Franciscan complex are aligned parallel to the active margin between the North American and Pacific plates. The Franciscan Complex is in contact with the Great Valley Sequence, which was deposited on the Coast Range Ophiolite, along its eastern side. The type area of Franciscan rocks in San Francisco consists of metagraywackes, gray claystone and shale, thin bedded ribbon chert with abundant radiolarians, altered submarine pillow basalts (greenstone) and blueschists. Broadly, the Franciscan can be divided into two groups of rocks. Coherent terranes are internally consistent in metamorphic grade and include folded and faulted clastic sediments, cherts and basalts, ranging from sub-metamorphic to prehnite-pumpellyite or low-temperature blueschist (jadeite-bearing) grades of metamorphism. Mélange terranes are much smaller, found between or within the larger coherent terranes and sometimes contain large blocks of metabasic rocks of higher metamorphic grade (amphibolite, eclogite, and garnet-blueschist). The mélange zones in the Franciscan usually have a block in matrix appearance with higher grade metamorphic blocks (blueschist, amphibolite, greenschist, eclogite) embedded within the mélange matrix. The matrix material of the mélanges are mudstone or serpentinite. Geologists have argued for either a tectonic or olistostormal origin. In the northern Coast Ranges, the Franciscan has been divided into the Eastern, Central and Coastal Belts based on metamorphic age and grade, with the rocks younging and the metamorphic grade decreasing to the west. The Franciscan varies along strike, because individual accreted elements (packets of trench sediment, seamounts, etc.) did not extend the full length of the trench. Different depths of underplating, distribution of post-metamorphic faulting, and level of erosion produced the present-day surface distribution of high P/T metamorphism. Gallery Fossils Franciscan sediments contain a sparse, but diverse assemblage of fossils. The most abundant fossils by far are microfossils, particularly in the cherts, which contain single-celled organisms called radiolarians that have exoskeletons of silica. There are also in some of the shales microfossils of planktonic foraminifera that have exoskeletons of carbonate. These microfossils, by and large, indicate deposition in an open-water setting where deep-water conditions exist. Vertebrate fossils in the Franciscan are extremely rare, but include three Mesozoic marine reptiles that are shown in the table below. Again, these indicate an open-water, and therefore deep-marine setting. Although rare, a few shallow-marine fossils have been found as well, and include extinct oysters (Inoceramus) and clams (Buchia). Microfossils in the Calera Limestone member of the