Sixty-two samples from well-established comagmatic granitoid sequences and certain unassigned formations and plutons of the central part of the Sierra Nevada batholith between latitudes 37° and 38° N. have been dated by the isotopic U-Pb method on zircon. The U-Pb ages indicate the following age distribution of the granitoids: (1) The axial part of the batholith is occupied by Cretaceous granitoid sequences that are progressively younger eastward over a 37-m.y. interval extending from about 125 m.y. to about 88 m.y. ago. (2) A single, but extensive, Triassic sequence with an optimum average age of about 210 m.y. is present in the east side of the batholith. (3) Plutons and granitoid sequences of Jurassic age, most of them with U-Pb ages between 186 and 155 m.y., occur in both margins and locally in the interior of the batholith. The distribution of Jurassic ages suggests that prior to the emplacement of the Cretaceous granitoids, Jurassic granitoids were widely distributed across the central Sierra Nevada but were not emplaced in a west-to-east succession as were the Cretaceous granitoids. Few of our ages fall between 155 and 125 m.y. However, a U-Pb age of 144 m.y. has been reported on the Sage Hen Flat pluton in the White Mountains, and U-Pb ages between 134 and 128 m.y. have been reported on remnants of older granitoids farther south in the Sierra Nevada, which are associated with roof pendants and septa. Also, numerous K-Ar ages on hornblende in the range of 152 to 131 m.y. have been reported on samples collected farther north along the west side of the batholith. The distribution of U-Pb ages is consistent with the interpretation that in the central Sierra Nevada, a belt of Cretaceous granitoids trending about N. 20° W. crosses a belt of Jurassic granitoids trending about N. 40° W. However, the U-Pb ages provide little support for the existence of five cyclic intrusive epochs for California and western Nevada. Comparison of the U-Pb ages on zircon with the K-Ar ages on biotite and hornblende shows generally good agreement for the younger granitoids but decreasing agreement for increasingly older granitoids. Most of the K-Ar ages on biotite and many on hornblende from older granitoids appear to have been reduced as a result of reheating by younger plutons. The dispersion of K-Ar ages reflects the complex structural and thermal history of the batholith.

The Psychiatric Consultation Service at Massachusetts General Hospital sees medical and surgical inpatients with comorbid psychiatric symptoms and conditions. Such consultations require the integration of medical and psychiatric knowledge. During their twice-weekly rounds, Dr Stern and other members of the Consultation Service discuss the diagnosis and management of conditions confronted. These discussions have given rise to rounds reports that will prove useful for clinicians practicing at the interface of medicine and psychiatry.Dr Unruh is an attending psychiatrist at McLean Hospital, Belmont, Massachusetts, and an instructor in psychiatry at Harvard Medical School, Boston, Massachusetts. Dr Nejad is an instructor in psychiatry at Harvard Medical School, Boston, Massachusetts, an attending physician on the Psychiatric Consultation Service at Massachusetts General Hospital, Boston, and the director of the Burns and Trauma Psychiatric Consultation Service at Massachusetts General Hospital, Boston. Mr Stern is a research assistant in the Department of Psychiatry at Massachusetts General Hospital, Boston. Dr Stern is chief of the Psychiatric Consultation Service at Massachusetts General Hospital, Boston, and a professor of psychiatry at Harvard Medical School, Boston, Massachusetts.Dr Stern is an employee of the Academy of Psychosomatic Medicine, has served on the speaker's board of Reed Elsevier, is a stock shareholder in WiFiMD (Tablet PC), and has received royalties from Mosby/Elsevier and McGraw Hill. Drs Unruh and Nejad and Mr Stern report no financial or other affiliations relevant to the subject of this article.

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